feat(lanes,git): publish a repo with no remote, and read a repo with no commits

What broke: a lane on a fresh `git init` repo had no working git surface.
`statusCounts` ran `rev-parse --short HEAD` unguarded, so `gitFacts` threw
and `GET /api/lanes/:id/git` answered `{available:false}` — the Changes
panel showed no header, and `commit`/`switch` 500'd through `isDirty`.
Add lane in Worktree mode accepted such a repo and left a `failed` row
behind, and a repo with commits but no remote had a permanently disabled
Push with no way to give it one short of a terminal.

What changed:
- worktree.js: an unborn HEAD is a normal state. `statusCounts` reports
  `head: null`; `gitFacts` reads the branch via `symbolic-ref`, an empty
  subject, and a new `unborn` field.
- git-ops.js: an 11th write, `publish` — `remote add origin -- <url>` then
  `push -u origin HEAD`, only with a commit (ENOCOMMITS) and NO remote at
  all (EREMOTEEXISTS, so it never re-points one), the url allowlisted by
  `validateRemoteUrl` (https without userinfo, ssh://, scp-like; refuses
  local paths, file://, ext::, fd::, git://, http://, leading `-`:
  EBADURL), and `origin` removed again when the push fails.
- POST /api/lanes/worktree answers 400 EEMPTYREPO for a repo with no
  commits instead of creating a row that can only fail.
- LaneGitBar: unborn repos show "no commits yet" and a commit-first hint;
  no remote offers Publish… with an inline URL box; a remote but no
  upstream relabels Push as "Publish branch". AddLaneModal disables Add
  on an empty repo and offers "Use as a Repo lane".
- The two tests that used an unborn repo to force a provisioning failure
  now use a `feat` ref clash, since that repo is refused up front.
- CLAUDE.md rule reworded to "the boring eleven" with publish's guards;
  docs/API.md, docs/LANES.md, ARCHITECTURE.md, server/README.md, openapi.

openapi.yaml

@@ -10718,7 +10718,7 @@ paths:
                     type: object
                     additionalProperties: true
         '400':
-          description: sourceRepo is relative, missing, or not a git repository.
+          description: 'EBADSOURCEREPO: sourceRepo is relative, missing, or not a git repository. EEMPTYREPO: it has no commits, so there is nothing to branch a worktree from (no lane row is created).'
           content:
             application/json:
               schema:
@@ -10807,7 +10807,7 @@ paths:
             type: integer
       responses:
         '200':
-          description: available:true with {branch, head, subject, dirty, untracked, files}, or available:false alone. files names the files behind those counts as {path, status, added, deleted} records, capped at 20; the counts themselves are never capped. status is the two-character `git status --porcelain` code and path is the new path for a rename; added/deleted come from one `git diff --numstat HEAD` and are null where git has no delta to report (untracked, binary, renamed, or no commit to diff against).
+          description: available:true with {branch, head, unborn, subject, dirty, untracked, files, hasRemote, upstream, ahead, behind}, or available:false alone. A repo with no commit yet is available with unborn:true, head:null and subject:"". files names the files behind those counts as {path, status, added, deleted} records, capped at 20; the counts themselves are never capped. status is the two-character `git status --porcelain` code and path is the new path for a rename; added/deleted come from one `git diff --numstat HEAD` and are null where git has no delta to report (untracked, binary, renamed, or no commit to diff against).
         '404':
           description: Lane not found.
   /api/lanes/{id}/runtime:
@@ -11188,7 +11188,7 @@ paths:
       tags:
         - Lanes
       summary: One git write on the lane's working copy
-      description: 'fetch (--all --prune), pull (ALWAYS --ff-only — a diverged branch is reported, never merged), push (-u <remote> HEAD, so only the branch the lane is on; remote = the branch''s upstream remote, else the only remote, else origin, else 400 ENOREMOTE), stage/unstage (per file), discard (per file; irreversible, so it REQUIRES confirm:true), stage-hunk / discard-hunk (ONE hunk of a tracked file''s `git diff HEAD`, named by its `@@` line and re-read server-side at the given context — the applied patch is always git''s own text, never one from the request; discard-hunk REQUIRES confirm:true; 400 EUNTRACKED for an untracked file, 409 EHUNKGONE when the hunk is no longer in the diff), commit (git add -A then commit -m <message>, or only:"staged" to take the index as it stands), switch (git switch, -c to create; refuses a dirty tree so an agent''s half-finished work is never carried onto another branch), and branch-create / branch-delete (create never switches; delete is `git branch -d`, refuses main/master/development/develop, the current branch and one held by another worktree). A path in the body must be one `git status` is reporting as changed, so no path outside the lane is reachable. Guarded and serialized per git index (the lane lock keyed on the worktree''s git dir, so two lanes sharing one index cannot collide on index.lock). Deliberately no merge, rebase, reset or stash: reset stays behind the destroy guard on POST /api/lanes/{id}/reset. Network actions are killed after 60s.'
+      description: 'fetch (--all --prune), pull (ALWAYS --ff-only — a diverged branch is reported, never merged), push (-u <remote> HEAD, so only the branch the lane is on; remote = the branch''s upstream remote, else the only remote, else origin, else 400 ENOREMOTE), stage/unstage (per file; staging a conflicted file that still has conflict markers is 400 EMARKERS), discard (per file; irreversible, so it REQUIRES confirm:true), stage-hunk / discard-hunk (ONE hunk of a tracked file''s `git diff HEAD`, named by its `@@` line and re-read server-side at the given context — the applied patch is always git''s own text, never one from the request; discard-hunk REQUIRES confirm:true; 400 EUNTRACKED for an untracked file, 409 EHUNKGONE when the hunk is no longer in the diff), commit (git add -A then commit -m <message>, or only:"staged" to take the index as it stands), switch (git switch, -c to create; refuses a dirty tree so an agent''s half-finished work is never carried onto another branch), branch-create / branch-delete (create never switches; delete is `git branch -d`, refuses main/master/development/develop, the current branch and one held by another worktree), publish (the ONE write whose destination comes from the request: `git remote add origin -- <url>` then `git push -u origin HEAD`, only in a repo with a commit and NO remote — it never re-points one; the url must be https:// without userinfo, ssh:// or scp-like user@host:path, and origin is removed again if the push fails), and merge / resolve / merge-commit / merge-abort (issue #45: merge a local or remote-tracking branch that exists — clean tree and a repo-root lane only, 400 ESUBDIR otherwise — answering conflicts:[paths] when it stops on conflicts; resolve {path, side: ours|theirs|done} a conflicted path, done refusing leftover markers with 400 EMARKERS; merge-commit is 409 ECONFLICTS while anything is unmerged; merge-abort REQUIRES confirm:true; pull/switch/merge/hunk actions are 409 EMERGING mid-merge). fetch/pull/push/publish needing a login answer 409 EGITAUTH with auth:{protocol,host,username,rejected}; resend with credentials:{protocol,host,username,password,remember} (a repo remote''s host only, else 400 EBADHOST). A path in the body must be one `git status` is reporting as changed, so no path outside the lane is reachable. Guarded and serialized per git index (the lane lock keyed on the worktree''s git dir, so two lanes sharing one index cannot collide on index.lock). Deliberately no rebase, reset or stash: reset stays behind the destroy guard on POST /api/lanes/{id}/reset. Network actions are killed after 60s.'
       operationId: runLaneGitAction
       parameters:
         - name: id
@@ -11214,6 +11214,7 @@ paths:
               - switch
               - branch-create
               - branch-delete
+              - publish
       requestBody:
         required: false
         content:
@@ -11221,6 +11222,9 @@ paths:
             schema:
               type: object
               properties:
+                url:
+                  type: string
+                  description: publish only; https:// (no userinfo), ssh:// or user@host:path, max 1024 chars.
                 message:
                   type: string
                   description: commit only; required, max 4000 chars.
@@ -11257,13 +11261,13 @@ paths:
                   description: discard and discard-hunk; the call is refused without it.
       responses:
         '200':
-          description: '{action, ok:true, output} — git''s own stdout+stderr.'
+          description: '{action, ok:true, output} — git''s own stdout+stderr; publish adds remote:"origin".'
         '400':
-          description: EBADACTION, EBADMESSAGE, EBADBRANCH, EBADPATH, ECONFIRM, EPROTECTED, ENOBRANCH, EBRANCHEXISTS, EBRANCHBUSY, EDIRTY, ENOCHANGES, ESTAGEDOUTSIDE or ENOREMOTE.
+          description: EBADACTION, EBADMESSAGE, EBADBRANCH, EBADPATH, ECONFIRM, EPROTECTED, ENOBRANCH, EBRANCHEXISTS, EBRANCHBUSY, EDIRTY, ENOCHANGES, ESTAGEDOUTSIDE, ENOREMOTE, EUNTRACKED, EBADURL, EREMOTEEXISTS, ENOCOMMITS, EBADHOST, EBADCRED, ESUBDIR, EBADSIDE or EMARKERS.
         '404':
           description: Lane not found.
         '409':
-          description: EGIT — git ran and refused (a rejected push, a credential failure, a diverged --ff-only pull); its stderr is appended to error.message.
+          description: EGIT — git ran and refused (a rejected push, a diverged --ff-only pull); its stderr is appended to error.message. EGITAUTH — the remote wants a login (carries auth). EHUNKGONE, EMERGING, ENOMERGE, ECONFLICTS.
         '500':
           description: Unexpected server-side failure.
   /api/lanes/{id}/{action}: