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/servers/mods_router.py

@@ -0,0 +1,101 @@
+"""Mod management endpoints — list available mods, set enabled mods."""
+from __future__ import annotations
+
+import logging
+from typing import Annotated
+
+from fastapi import APIRouter, Depends, HTTPException, status
+from pydantic import BaseModel
+from sqlalchemy.engine import Connection
+
+from adapters.exceptions import AdapterError
+from adapters.registry import GameAdapterRegistry
+from core.dal.config_repository import ConfigRepository
+from core.servers.service import ServerService
+from database import get_db
+from dependencies import get_current_user, require_admin
+
+logger = logging.getLogger(__name__)
+
+router = APIRouter(prefix="/servers/{server_id}/mods", tags=["mods"])
+
+
+def _ok(data):
+    return {"success": True, "data": data, "error": None}
+
+
+class SetEnabledModsRequest(BaseModel):
+    mods: list[str]
+
+
+def _get_mod_manager(server_id: int, game_type: str):
+    """Get ModManager for the server's game type."""
+    adapter = GameAdapterRegistry.get(game_type)
+    if not adapter.has_capability("mod_manager"):
+        raise HTTPException(
+            status_code=status.HTTP_400_BAD_REQUEST,
+            detail={"code": "NOT_SUPPORTED", "message": f"Game type '{game_type}' does not support mod management"},
+        )
+    return adapter.get_mod_manager(server_id)
+
+
+@router.get("")
+def list_mods(
+    server_id: int,
+    db: Annotated[Connection, Depends(get_db)],
+    _user: Annotated[dict, Depends(get_current_user)],
+) -> dict:
+    """List all available mods and which are enabled."""
+    server = ServerService(db).get_server(server_id)  # raises 404 if not found
+    mgr = _get_mod_manager(server_id, server["game_type"])
+
+    config_repo = ConfigRepository(db)
+    try:
+        available = mgr.list_available_mods()
+        enabled = set(mgr.get_enabled_mods(config_repo))
+    except AdapterError as exc:
+        raise HTTPException(status_code=500, detail={"code": "ADAPTER_ERROR", "message": str(exc)})
+
+    for mod in available:
+        mod["enabled"] = mod["name"] in enabled
+
+    return _ok({
+        "server_id": server_id,
+        "mods": available,
+        "enabled_count": len(enabled),
+    })
+
+
+@router.put("/enabled")
+def set_enabled_mods(
+    server_id: int,
+    body: SetEnabledModsRequest,
+    db: Annotated[Connection, Depends(get_db)],
+    _admin: Annotated[dict, Depends(require_admin)],
+) -> dict:
+    """
+    Set the list of enabled mods.
+    Replaces the current enabled list entirely.
+    Server must be restarted for changes to take effect.
+    """
+    server = ServerService(db).get_server(server_id)  # raises 404 if not found
+    mgr = _get_mod_manager(server_id, server["game_type"])
+
+    config_repo = ConfigRepository(db)
+    try:
+        mgr.set_enabled_mods(body.mods, config_repo)
+    except AdapterError as exc:
+        raise HTTPException(status_code=400, detail={"code": "ADAPTER_ERROR", "message": str(exc)})
+    except ValueError as exc:
+        if "CONFIG_VERSION_CONFLICT" in str(exc):
+            raise HTTPException(
+                status_code=status.HTTP_409_CONFLICT,
+                detail={"code": "VERSION_CONFLICT", "message": "Config was modified by another request. Please retry."},
+            )
+        raise
+    db.commit()
+
+    return _ok({
+        "message": "Enabled mods updated. Restart the server for changes to take effect.",
+        "enabled_mods": body.mods,
+    })