feat: runtime and UX polish

P1 features:
- System prompt injection on session resume (ThreadRecord gains system_prompt
  field, ensure_engine_loaded passes it to Op::SyncSession)
- Session resume bridge: GET/POST /v1/sessions/{id}, seed_thread_from_messages
- Task detail panel with deep links (?task=<id>), timeline, tool calls
- Tauri desktop build fix (CI=true in tauri:build script)

P2 features:
- Task detail auto-refresh polling for running/queued tasks (3s interval)
- Session delete: DELETE /v1/sessions/{id} endpoint + palette delete button
- Transcript full-text search input with combined role filter + search
- Per-item copy-to-clipboard, collapse/expand for long outputs, filter chips

Polish:
- Typography scale CSS variables, skeleton loading utilities
- Panel slide-in animation for task detail, fade-up for list items
- Toast auto-dismiss (4s success, 6s error) with dismiss buttons
- Focus trap in command palette, backdrop click to close
- Escape key closes task detail panel
- ARIA improvements: role=alert on error toasts, role=listbox on palette
- Responsive breakpoints for tablet (task detail stacking, palette width)
- prefers-reduced-motion respected throughout

All validation checks pass:
- cargo test (517 tests), cargo check
- pnpm typecheck, lint (0 errors), test (36 tests)
- pnpm web:build, desktop:build

.gitignore

@@ -11,6 +11,7 @@
 # Development
 .env
 .env.*
+node_modules/
 .vscode/
 .idea/
 *.swp