feat(projects): worktree remove + prune from any device (W4)

Closes the create-only loop — delete losing worktrees and prune stale ones without
a terminal. Destructive, so guarded hard:

- src/http/worktrees.ts: removeWorktree + pruneWorktrees (execFile, no shell, never
  rm -rf; git worktree remove [--force] / git worktree prune). Safeguards:
  (1) target realpath must match an entry git itself reports in `git worktree list`
  for THIS repo → 404 otherwise (arbitrary FS paths never match, so git is never
  invoked against them); (2) reject the MAIN worktree → 400; (3) realpath
  containment on request + each list entry, operating on git's canonical path (+ --);
  (4) dirty tree without force → 409 "force required"; (5) locked → 409; (6) errors
  classified to fixed safe strings (raw stderr/paths never leaked).
- DELETE /projects/worktree + POST /projects/worktree/prune — both behind
  requireAllowedOrigin + worktreeEnabled + audit-logged, mirroring the create route.
- public/projects.ts: ✕ remove button per linked-worktree row (hidden for main/locked)
  + a prune button; force needs an explicit second confirm (no single-click data loss).

Verified: typecheck + build:web clean, worktree tests 108 pass (unit covers
reject-non-registered / reject-main / reject-escape / refuse-dirty-without-force /
clean-remove / force-remove / prune), full suite green at --test-timeout=30000.

src/types.ts

@@ -594,6 +594,26 @@ export interface CreateWorktreeResult {
   error?: string;
 }
 
+/** Result of DELETE /projects/worktree (W4 remove). `error` is a SAFE message
+ *  only (never raw git stderr, SEC-M10); `status` is the HTTP status to return.
+ *  `path` echoes git's own canonical worktree path that was removed. */
+export interface RemoveWorktreeResult {
+  ok: boolean;
+  path?: string;
+  status?: number;
+  error?: string;
+}
+
+/** Result of POST /projects/worktree/prune (W4). `pruned` lists best-effort
+ *  human labels of the stale worktrees git reclaimed (empty = nothing to prune,
+ *  idempotent). `error` is a SAFE message only (SEC-M10). */
+export interface PruneWorktreesResult {
+  ok: boolean;
+  pruned?: string[];
+  status?: number;
+  error?: string;
+}
+
 /* ── v0.6 Projects UI preferences (server-persisted, cross-device) ── */
 
 /** Cross-device UI preferences for the Projects launcher (impl: src/http/prefs-store.ts).