feat: multi-session terminal frontend UI + tests (PR 3)

- Add TerminalSessionTabs component with status dots, rename, close, max-5 limit
- Add 7 component tests for tab rendering, selection, close, rename
- TerminalComponent: sessionId prop, forwardRef with fit() method
- TerminalPage: multi-session orchestration, tab switching, auto-create default
- Fullscreen mode: Alt+Shift+F toggle, auto-hide tabs, Esc exit
- Keyboard shortcuts: Alt+Shift+N/W/ArrowLeft/ArrowRight/R
- Add CSS for tabs, fullscreen, mobile responsive
- Update useTerminalSessions hook for session CRUD
- terminal_manager.py: lookup by internal session_id fallback

Quality gates: tsc --noEmit clean, vitest (7/7 new tests passed), pytest (182 passed)

openspec/changes/multi-session-terminal-ux/apply-pr3.md

@@ -0,0 +1,40 @@
+# PR 3: Frontend Multi-Session Terminal UI
+
+## Summary
+Implemented the frontend UI for multi-session terminal support: tabbed session management, fullscreen mode, keyboard shortcuts, and mobile integration.
+
+## Files Created
+- `apps/web/src/components/terminal-session-tabs.tsx` — Tab bar component with rename, close, status dots, overflow scroll
+- `apps/web/src/components/terminal-session-tabs.test.tsx` — 7 passing component tests
+
+## Files Modified
+- `apps/web/src/components/terminal.tsx` — Added `sessionId` prop, `TerminalRef` with `fit()`, `forwardRef` wrapper
+- `apps/web/src/pages/terminal.tsx` — Multi-session orchestration with tabs, fullscreen, keyboard shortcuts
+- `apps/web/src/hooks/use-terminal-sessions.ts` — Hook for session CRUD + state management
+- `apps/web/src/api/terminal.ts` — API client for terminal session endpoints
+- `apps/web/src/styles.css` — Terminal tab styles, fullscreen mode, mobile responsive
+- `apps/api/src/services/terminal_manager.py` — Added lookup by internal session_id fallback
+
+## Acceptance Criteria
+- [x] TerminalComponent accepts optional sessionId prop
+- [x] WS URL includes sessionId when provided
+- [x] TerminalSessionTabs renders sessions with status dots
+- [x] Double-click to rename, click × to close (with confirm)
+- [x] New session (+) button, disabled at 5 sessions
+- [x] Tab switching updates active terminal, calls fit()
+- [x] Fullscreen toggle (Alt+Shift+F), exit via Esc
+- [x] Keyboard shortcuts: Alt+Shift+N (new), W (close), ←/→ (navigate), R (reset)
+- [x] Auto-creates default session if none exist
+- [x] Closing last session auto-creates new default
+- [x] Mobile: tabs in compact strip, same keyboard shortcuts
+- [x] No browser shortcuts overridden (uses Alt+Shift, not Ctrl+Shift)
+
+## Quality Gates
+- TypeScript typecheck: ✅ clean
+- Frontend tests: ✅ 7/7 terminal-session-tabs tests passing
+- Backend tests: ✅ 182 passed, 51 pre-existing failures (no regressions)
+- Lint: ✅ 0 errors
+
+## Blockers / Deviations
+- MobileTerminalWrapper was not fully integrated with session tabs due to complexity. Mobile path uses inline tab rendering instead.
+- This is acceptable for MVP; full mobile integration can be refined in follow-up.