feat(worktrees): create, list and remove git worktrees of a local case

Sessions in one case share its folder, so several agents on one repository
edit, build and commit in the same checkout and step on each other. A case
whose folder is a git repository can now keep worktrees under
<repo>/.claude/worktrees/<name> on a new branch (default worktree-<name>),
which is Claude Code's own --worktree layout (measured in Claude Code
2.1.296) and the one Codeman's worktree pill already recognizes.

New module src/git-worktrees.ts (pure name/branch gates, worktree list
parsing, exclude text; IO through an injectable runner) and routes
GET/POST /api/cases/:name/worktrees and
DELETE /api/cases/:name/worktrees/:worktree:

- git runs as argv with -- before paths, non-interactive env, process
  group timeouts, --no-optional-locks on reads; names are gated before
  git and confirmed with git check-ref-format --branch.
- Only <repo>/.claude/worktrees/<valid-name> is created or removed; every
  path component is lstat'ed and realpath-checked, so a symlinked .claude
  cannot redirect a create or remove outside the repository.
- /.claude/worktrees/ (and the per-workspace hooks file Codeman writes,
  which otherwise blocks git worktree remove) go to the repository's
  local info/exclude, never a tracked .gitignore.
- Removal is git worktree remove WITHOUT --force, refused while a live
  session runs inside; branch delete is git branch -d, never -D.
- Docker and remote cases are refused with a 400, and git never runs for
  a case at or inside a Docker case workspace.

Starting a session reuses the existing create paths: quick-start takes
a worktree name (validated, local cases only) and runs hooks, the skill,
the model override and the session itself in the worktree;
POST /api/sessions takes the worktree as workingDir. The unified session
list names the worktree of a live session from its folder layout, so a
codex or shell session in one gets the worktree pill too.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

src/web/server.ts

@@ -191,6 +191,7 @@ import {
   registerStatusTelemetryRoutes,
   registerSystemRoutes,
   registerCaseRoutes,
+  registerWorktreeRoutes,
   registerSessionRoutes,
   registerRespawnRoutes,
   registerRalphRoutes,
@@ -1153,6 +1154,7 @@ export class WebServer extends EventEmitter {
     registerStatusTelemetryRoutes(this.app, ctx);
     registerSystemRoutes(this.app, ctx);
     registerCaseRoutes(this.app, ctx);
+    registerWorktreeRoutes(this.app, ctx);
     // The registry's lifetime is the server's: it drops per-session wake state on every
     // cleanup path and resolves in-flight wakes on shutdown.
     this.remoteWake = registerSessionRoutes(this.app, ctx);