feat: comprehensive test infrastructure improvements

- Fix unit test imports: add env setup in conftest.py before module imports
- Add 24 new auth router tests (RBAC, preferences, password validation)
- Add 16 new tests for litellm and chat_summary routers
- Apply black formatting and ruff linting across codebase
- Add pre-commit hooks configuration (black, ruff, file checks)
- Increase CI coverage threshold from 40% to 50%

Test Results:
- 206 tests passing (91 unit + 115 integration)
- Coverage: 58.79% on core modules
- auth.py: 57% → 85%, litellm.py: 23% → 87%, chat_summary.py: 41% → 100%
- auth_service: 96.51%, config: 100%, rbac: 93.48%

dashboard/backend/routers/system.py

@@ -1,12 +1,14 @@
 import os
-import shutil
-import psutil
 import platform
+import shutil
 import time
+
 import httpx
-from fastapi import APIRouter, Query, Request, HTTPException
+import psutil
+from fastapi import APIRouter, HTTPException, Query, Request
+
 import config
-from config import TELEGRAM_BOT_TOKEN, TELEGRAM_CHAT_ID, VOLUME_ROOT, OPENCLAW_GATEWAY_TOKEN
+from config import OPENCLAW_GATEWAY_TOKEN, TELEGRAM_BOT_TOKEN, TELEGRAM_CHAT_ID, VOLUME_ROOT
 
 router = APIRouter()
 
@@ -36,7 +38,15 @@ def system_stats():
             seen_devices.add(mount.device)
             try:
                 u = shutil.disk_usage(mount.mountpoint)
-                volumes.append({"mount": mount.mountpoint, "total": u.total, "used": u.used, "free": u.free, "percent": round(u.used / u.total * 100, 1)})
+                volumes.append(
+                    {
+                        "mount": mount.mountpoint,
+                        "total": u.total,
+                        "used": u.used,
+                        "free": u.free,
+                        "percent": round(u.used / u.total * 100, 1),
+                    }
+                )
             except Exception:
                 pass
     mem = psutil.virtual_memory()
@@ -90,7 +100,18 @@ def audit_log(lines: int = Query(100, le=500)):
         level = _classify(method, path, status, user)
         if level == "noise":
             continue
-        entries.append({"ts": ts, "ip": ip, "user": user, "method": method, "path": path, "status": status, "duration": dur, "level": level})
+        entries.append(
+            {
+                "ts": ts,
+                "ip": ip,
+                "user": user,
+                "method": method,
+                "path": path,
+                "status": status,
+                "duration": dur,
+                "level": level,
+            }
+        )
     return {"entries": entries}