feat(lanes,ui): per-lane git surface — Changes panel, VS Code-style diff, branch-aware Add lane, redesigned tooltips (#34, #35)

- Changes card beside lane detail with five modes: Files tree, overview,
  Review (whole diff, per-file collapse), single file, commit history.
- LaneDiffView: unified / side-by-side with independent scroll on both axes
  and mirrored scrollLeft, expand/collapse context, intra-line emphasis.
- Staged-only commit box; git actions (fetch/pull/push/stage/unstage/
  discard/commit/switch/branch-create/branch-delete) guarded in git-ops.js.
- Server: git-diff.js + git-ops.js behind GET /api/lanes/:id/git/* and
  POST /api/lanes/:id/git/:action; gitFacts gains upstream/ahead/behind.
- Add lane: new/existing branch, current branch, worktree list, prefill
  from the git bar's "New lane here"; /api/run/cwds gains a repo kind.
- GlobalTooltip upgrades every native title into a themed anchored bubble;
  chart/info popovers use theme tokens.

server/README.md

@@ -524,6 +524,14 @@ 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/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`. |
+| `GET` | `/api/lanes/:id/git/ls?q=` | Tracked paths matching a substring, for quick-open. `git ls-files`, so ignored files never appear. Capped at 500. |
+| `GET` | `/api/lanes/:id/git/tree?path=` | One directory level of tracked files, folded. `400 EBADPATH` for a path escaping the lane. |
+| `GET` | `/api/lanes/:id/git/branches` | The lane repo's own local branches + worktrees, for the branch switcher. The repo comes from the lane row, never the query. |
+| `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`), `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). No merge/rebase/reset/stash by design. |
 
 The route accepts `{ sourceRepo, title, base?, slug? }`. `sourceRepo` must be
 an existing absolute git repository. The response lane starts as