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/utils/port_checker.py

@@ -0,0 +1,87 @@
+"""Game-agnostic port availability checking."""
+from __future__ import annotations
+
+import logging
+import socket
+
+logger = logging.getLogger(__name__)
+
+
+def is_port_in_use(port: int, host: str = "127.0.0.1") -> bool:
+    """Return True if the port is already bound."""
+    with socket.socket(socket.AF_INET, socket.SOCK_STREAM) as s:
+        s.settimeout(0.5)
+        try:
+            s.bind((host, port))
+            return False
+        except OSError:
+            return True
+
+
+def check_server_ports_available(
+    game_port: int,
+    rcon_port: int | None = None,
+    host: str = "127.0.0.1",
+    port_conventions: dict[str, int] | None = None,
+) -> list[int]:
+    """
+    Check all ports for a server instance.
+    If port_conventions is provided (from adapter), checks all derived ports.
+    Returns list of ports that are already in use (empty = all available).
+    """
+    ports_to_check: set[int] = set()
+
+    if port_conventions:
+        ports_to_check.update(port_conventions.values())
+    else:
+        ports_to_check.add(game_port)
+
+    if rcon_port is not None:
+        ports_to_check.add(rcon_port)
+
+    return [p for p in sorted(ports_to_check) if is_port_in_use(p, host)]
+
+
+def check_ports_against_running_servers(
+    new_server_game_port: int,
+    new_server_rcon_port: int | None,
+    exclude_server_id: int | None,
+    db,
+) -> list[int]:
+    """
+    Cross-game port conflict detection.
+    Checks new server's full port set against all running servers' full port sets.
+    Returns list of conflicting ports.
+    """
+    from adapters.registry import GameAdapterRegistry
+    from sqlalchemy import text
+
+    rows = db.execute(
+        text("SELECT id, game_type, game_port, rcon_port FROM servers WHERE status IN ('running','starting')")
+    ).fetchall()
+
+    occupied_ports: set[int] = set()
+    for row in rows:
+        if exclude_server_id and row[0] == exclude_server_id:
+            continue
+        try:
+            adapter = GameAdapterRegistry.get(row[1])
+            conventions = adapter.get_process_config().get_port_conventions(row[2])
+            occupied_ports.update(conventions.values())
+        except KeyError:
+            logger.debug("Unknown game type '%s', falling back to game_port only", row[1])
+            occupied_ports.add(row[2])
+        if row[3] is not None:
+            occupied_ports.add(row[3])
+
+    # Check new server's ports against occupied set
+    try:
+        adapter = GameAdapterRegistry.get("arma3")  # temporary — will be passed in
+    except KeyError:
+        logger.debug("No 'arma3' adapter for port conventions, using defaults")
+
+    new_ports: set[int] = {new_server_game_port}
+    if new_server_rcon_port:
+        new_ports.add(new_server_rcon_port)
+
+    return sorted(new_ports & occupied_ports)