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.

README.md

@@ -42,6 +42,13 @@ Internal build — all rights reserved.
   terminal too via `agenthub lanes shell`. Which CLI it starts is the lane's own
   setting. **This is the part that needs `tmux` installed** — see
   [Prerequisites](#prerequisites).
+- **Git, from the dashboard.** Each lane card shows its branch, `↑ahead ↓behind`
+  and its uncommitted files, with buttons for the ordinary moves: fetch, pull
+  (always `--ff-only`), push, commit-all, and switching branch on a clean tree.
+  Beside the lane sits a collapsible **Changes** panel — an overview of the
+  changed files, a full review of every diff, or one file at a time, comparing
+  either uncommitted work or the whole branch against its base. There is no
+  merge/rebase/reset button by design: recovery from those needs a terminal.
 - **Per-lane app stacks.** A repo that declares `.agenthub/profile/` gets its own
   slot, ports and services per lane (`agenthub lanes up|down|logs`).
 - **Ship pipelines.** `/agenthub:ship-full` and `/agenthub:ship-quick` drive a
@@ -278,7 +285,9 @@ lane. This is resource namespacing on the host, not a container: lanes run as th
 same user and share the network.
 
 [`docs/LANES.md`](docs/LANES.md) has the pipeline model, the destroy guard, the
-preflight contract, the Workspace page, `GET /api/lanes/:id/git`, and the full
+preflight contract, the Workspace page, the git surface (`GET /api/lanes/:id/git`,
+`/git/changes`, `/git/log`, `/git/file`, `/git/ls`, `/git/tree`,
+`POST /:id/git/:action`), and the full
 runtime/profile contract.
 
 ## Tests