feat: implement full backend + frontend server detail, settings, and create server pages

Backend:
- Complete FastAPI backend with 42+ REST endpoints (auth, servers, config,
  players, bans, missions, mods, games, system)
- Game adapter architecture with Arma 3 as first-class adapter
- WebSocket real-time events for status, metrics, logs, players
- Background thread system (process monitor, metrics, log tail, RCon poller)
- Fernet encryption for sensitive config fields at rest
- JWT auth with admin/viewer roles, bcrypt password hashing
- SQLite with WAL mode, parameterized queries, migration system
- APScheduler cleanup jobs for logs, metrics, events

Frontend:
- Server Detail page with 7 tabs (overview, config, players, bans,
  missions, mods, logs)
- Settings page with password change and admin user management
- Create Server wizard (4-step; known bug: silent validation failure)
- New hooks: useServerDetail, useAuth, useGames
- New components: ServerHeader, ConfigEditor, PlayerTable, BanTable,
  MissionList, ModList, LogViewer, PasswordChange, UserManager
- WebSocket onEvent callback for real-time log accumulation
- 120 unit tests passing (Vitest + React Testing Library)

Docs:
- Added .gitignore, CLAUDE.md, README.md
- Updated FRONTEND.md, ARCHITECTURE.md with current implementation state
- Added .env.example for backend configuration

Known issues:
- Create Server form: "Next" buttons don't validate before advancing,
  causing silent submit failure when fields are invalid
- Config sub-tabs need UX redesign for non-technical users

backend/core/jobs/scheduler.py

@@ -0,0 +1,40 @@
+"""
+APScheduler setup for background cleanup jobs.
+
+One scheduler instance runs per process.
+Jobs run in their own threads (ThreadPoolExecutor).
+"""
+from __future__ import annotations
+
+import logging
+
+from apscheduler.schedulers.background import BackgroundScheduler
+from apscheduler.executors.pool import ThreadPoolExecutor
+
+logger = logging.getLogger(__name__)
+
+_scheduler: BackgroundScheduler | None = None
+
+
+def get_scheduler() -> BackgroundScheduler:
+    global _scheduler
+    if _scheduler is None:
+        _scheduler = BackgroundScheduler(
+            executors={"default": ThreadPoolExecutor(max_workers=2)},
+            job_defaults={"coalesce": True, "max_instances": 1},
+        )
+    return _scheduler
+
+
+def start_scheduler() -> None:
+    sched = get_scheduler()
+    if not sched.running:
+        sched.start()
+        logger.info("APScheduler started")
+
+
+def stop_scheduler() -> None:
+    global _scheduler
+    if _scheduler is not None and _scheduler.running:
+        _scheduler.shutdown(wait=False)
+        logger.info("APScheduler stopped")