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.

test/worktrees.test.ts

@@ -0,0 +1,83 @@
+/**
+ * test/worktrees.test.ts — parseWorktrees (pure parser for `git worktree list
+ * --porcelain`). The git wrapper itself is covered via the projects-detail
+ * integration test in projects.test.ts.
+ */
+
+import { describe, it, expect } from 'vitest'
+import { parseWorktrees } from '../src/http/worktrees.js'
+
+const MAIN = [
+  'worktree /repo/main',
+  'HEAD 1234567890abcdef1234567890abcdef12345678',
+  'branch refs/heads/main',
+  '',
+].join('\n')
+
+describe('parseWorktrees', () => {
+  it('parses a single main worktree on a branch', () => {
+    const wts = parseWorktrees(MAIN, '/repo/main')
+    expect(wts).toHaveLength(1)
+    expect(wts[0]).toMatchObject({
+      path: '/repo/main',
+      branch: 'main',
+      head: '12345678', // first 8 of the sha
+      isMain: true,
+      isCurrent: true,
+    })
+  })
+
+  it('marks only the first record as main; flags the current path', () => {
+    const text = [
+      'worktree /repo/main',
+      'HEAD aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa',
+      'branch refs/heads/main',
+      '',
+      'worktree /repo/wt/feature',
+      'HEAD bbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbb',
+      'branch refs/heads/feature/login',
+      '',
+    ].join('\n')
+    const wts = parseWorktrees(text, '/repo/wt/feature')
+    expect(wts).toHaveLength(2)
+    expect(wts[0]).toMatchObject({ path: '/repo/main', branch: 'main', isMain: true, isCurrent: false })
+    expect(wts[1]).toMatchObject({
+      path: '/repo/wt/feature',
+      branch: 'feature/login', // refs/heads/ stripped, slashes kept
+      isMain: false,
+      isCurrent: true,
+    })
+  })
+
+  it('handles a detached HEAD (no branch)', () => {
+    const text = ['worktree /repo/x', 'HEAD cccccccccccccccccccccccccccccccccccccccc', 'detached', ''].join('\n')
+    const wts = parseWorktrees(text, '/other')
+    expect(wts[0]?.branch).toBeUndefined()
+    expect(wts[0]?.head).toBe('cccccccc')
+  })
+
+  it('captures locked and prunable flags', () => {
+    const text = [
+      'worktree /repo/locked',
+      'HEAD dddddddddddddddddddddddddddddddddddddddd',
+      'branch refs/heads/wip',
+      'locked',
+      'prunable gitdir file points to non-existent location',
+      '',
+    ].join('\n')
+    const wts = parseWorktrees(text, '/x')
+    expect(wts[0]?.locked).toBe(true)
+    expect(wts[0]?.prunable).toBe(true)
+  })
+
+  it('parses the final record even without a trailing blank line', () => {
+    const text = ['worktree /repo/main', 'HEAD eeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeee', 'branch refs/heads/main'].join(
+      '\n',
+    )
+    expect(parseWorktrees(text, '/repo/main')).toHaveLength(1)
+  })
+
+  it('returns [] for empty input', () => {
+    expect(parseWorktrees('', '/x')).toEqual([])
+  })
+})