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.

server/README.md

@@ -524,7 +524,7 @@ Request body shape:
 | `POST` | `/api/lanes/:id/down` | Same-origin guarded stack teardown: recorded pid trees, then a port backstop only when a pid file existed. |
 | `POST` | `/api/lanes/:id/hook/:name` | Same-origin guarded profile-hook run; `:name` must be in the fixed hook allowlist and `args` is passed as argv. Returns `202`. |
 | `GET` | `/api/lanes/:id/logs/:svc` | Tail a hook or service log, `realpath`-confined to the lane's log directory. |
-| `GET` | `/api/lanes/:id/git` | Working-copy facts: branch, head, subject, uncommitted counts and files, plus `hasRemote`/`upstream`/`ahead`/`behind` (null counts when the branch has no upstream). `{available:false}` with `200` for a cwd git cannot read. |
+| `GET` | `/api/lanes/:id/git` | Working-copy facts: branch, head, subject, uncommitted counts and files, plus `hasRemote`/`upstream`/`ahead`/`behind` (null counts when the branch has no upstream), and `unborn` (`true` with `head: null` in a repo with no commit yet). `{available:false}` with `200` for a cwd git cannot read. |
 | `GET` | `/api/lanes/:id/git/changes?range=work\|branch\|commit[&sha=][&path=][&full=1][&context=]` | The lane's code changes for the Changes panel: a file summary, one file's hunks (`path`), or every file's hunks (`full=1`); `range=commit&sha=` is one commit, `context=` (default 3, max 5000) widens each hunk. Capped at 300 files / 200 KB per file / 1 MB per full read. `400 ENOBASE`, `ENOFILECHANGE`, `EBADRANGE` or `EBADREV`. |
 | `GET` | `/api/lanes/:id/git/log?limit=&file=` | The lane's recent commits (newest first, limit max 200), optionally only those touching one path. |
 | `GET` | `/api/lanes/:id/git/file?path=&rev=` | One file's whole content at `work` (realpath-confined to the lane), `HEAD` or a commit-ish. 1 MB cap. `400 EBADPATH`/`EBADREV`/`ENOFILE`. |
@@ -535,7 +535,7 @@ Request body shape:
 | `GET` | `/api/git-credentials` | AgentHub's own git logins (one per host, shared by every user), `hasToken` only — never a password. |
 | `POST` | `/api/git-credentials` | Same-origin guarded save/replace: `{protocol, host, username, password}`. `400 EBADHOST`/`EBADCRED`. |
 | `DELETE` | `/api/git-credentials/:protocol/:host` | Same-origin guarded delete. `404 ENOTFOUND`. |
-| `POST` | `/api/lanes/:id/git/:action` | Same-origin guarded git write, serialized under the lane lock: `fetch`, `pull` (always `--ff-only`), `push` (`-u origin HEAD`), `stage`/`unstage`/`discard` (per file; a path must be one git reports changed, and `discard` needs `confirm:true`), `stage-hunk`/`discard-hunk` (one hunk by its `@@` line, re-read fresh — `409 EHUNKGONE` when it moved; `discard-hunk` needs `confirm:true`), `commit` (`add -A` + `-m`, or `only:"staged"`), `switch` (refuses a dirty tree), `branch-create` (never switches) and `branch-delete` (`-d`, refuses protected/current/busy branches). `merge` (clean tree, repo-root lane, a ref that exists; conflicts come back as `conflicts[]`), `resolve` (`side: ours|theirs|done`, conflicted paths only, `done` refuses leftover markers), `merge-commit`, `merge-abort` (`confirm:true`); `EMERGING` blocks pull/switch/merge/hunk actions mid-merge. No rebase/reset/stash by design. A remote wanting a login is `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`; saved only after git succeeds and `remember` is set). |
+| `POST` | `/api/lanes/:id/git/:action` | Same-origin guarded git write, serialized under the lane lock: `fetch`, `pull` (always `--ff-only`), `push` (`-u origin HEAD`), `stage`/`unstage`/`discard` (per file; a path must be one git reports changed, and `discard` needs `confirm:true`), `stage-hunk`/`discard-hunk` (one hunk by its `@@` line, re-read fresh — `409 EHUNKGONE` when it moved; `discard-hunk` needs `confirm:true`), `commit` (`add -A` + `-m`, or `only:"staged"`), `switch` (refuses a dirty tree), `branch-create` (never switches) `branch-delete` (`-d`, refuses protected/current/busy branches) and `publish` (`{url}`: `remote add origin` + `push -u origin HEAD`, only when the repo has no remote; URL allowlisted to https-without-userinfo/ssh/scp-like; remote rolled back on a failed push). `merge` (clean tree, repo-root lane, a ref that exists; conflicts come back as `conflicts[]`), `resolve` (`side: ours|theirs|done`, conflicted paths only, `done` refuses leftover markers), `merge-commit`, `merge-abort` (`confirm:true`); `EMERGING` blocks pull/switch/merge/hunk actions mid-merge. No rebase/reset/stash by design. A remote wanting a login is `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`; saved only after git succeeds and `remember` is set). |
 
 The route accepts `{ sourceRepo, title, base?, slug? }`. `sourceRepo` must be
 an existing absolute git repository. The response lane starts as