feat(v0.6): per-project detail view — branch/worktrees + active sessions

Clicking a project's name opens an in-app detail view (back button returns to
the grid) with:
- header: name, path, branch, dirty
- Branch / Worktrees: each `git worktree list` entry (branch or detached@head,
  main/current/locked/prunable tags, path) — a single-worktree repo shows its
  branch; a multi-worktree repo shows them all
- Active sessions (N): detailed rows (status, devices watching, started-ago)
  with Open + Kill
- the Claude/Codex/VS Code launcher row

Backend: src/http/worktrees.ts (parseWorktrees pure + listWorktrees via
execFile, no shell, best-effort); buildProjectDetail(cfg, path, liveSessions)
in projects.ts (validates absolute existing dir, reuses branch/dirty/session
helpers, uncached — detail is on-demand and wants fresh state); read-only
GET /projects/detail?path= (no Origin guard, like /projects; 400 missing /
404 invalid). Types: WorktreeInfo, ProjectDetail.

Frontend: detail view + navigation in projects.ts (grid<->detail), project
name becomes a link, Kill via DELETE /live-sessions/:id.

Tests +21 (452 total): worktree parser, buildProjectDetail (validation,
non-git, session merge, real git-init worktree), renderProjectDetail.
worktrees.ts 100% / projects.ts 93.8% cov. Verified in-browser: opened a
Claude session, then the detail showed its branch+worktree and the live
session with Open/Kill.

src/types.ts

@@ -223,6 +223,29 @@ export interface ProjectInfo {
   sessions: ProjectSessionRef[]; // running sessions in this project (1:N; may be empty)
 }
 
+/** One entry from `git worktree list --porcelain` (project detail view). */
+export interface WorktreeInfo {
+  path: string; // worktree absolute path
+  branch?: string; // branch name (refs/heads/x → x); undefined when detached
+  head?: string; // short HEAD sha
+  isMain: boolean; // the repo's primary worktree (listed first)
+  isCurrent: boolean; // this worktree is the requested project path
+  locked?: boolean; // `git worktree lock`ed
+  prunable?: boolean; // git considers it prunable (gone working tree)
+}
+
+/** Detailed view of one project: branch/worktrees + its running sessions.
+ *  impl: src/http/projects.ts buildProjectDetail(cfg, path, liveSessions). */
+export interface ProjectDetail {
+  name: string;
+  path: string;
+  isGit: boolean;
+  branch?: string;
+  dirty?: boolean;
+  worktrees: WorktreeInfo[]; // empty for a non-git dir
+  sessions: ProjectSessionRef[]; // running sessions under this path (fresh)
+}
+
 export interface SessionManager {
   handleAttach(
     ws: WebSocketLike,