security: fix critical vulnerabilities (issues #2 and #3)

Issue #2: Unprotected Chat Summary Trigger (CRITICAL)
- Add authentication and admin authorization to /trigger endpoint
- Add path validation to prevent directory traversal
- Block access to system directories (/etc, /root, /sys, /proc, /boot)
- Add tests for unauthorized access and invalid paths

Issue #3: Exception Information Disclosure (HIGH)
- Replace raw exception messages with generic errors
- Log full exception details server-side with logger.exception()
- Affected files: auth.py, files.py, passkey.py, opc_agents.py
- Prevents information leakage about system architecture

Security Impact:
- Prevents unauthenticated file system writes
- Reduces reconnaissance opportunities for attackers
- Maintains security while preserving debugging capability

Tests: 214 passing, all security tests verified

dashboard/backend/routers/files.py

@@ -1,3 +1,4 @@
+import logging
 import os
 import re
 import shutil
@@ -10,6 +11,7 @@ from config import VOLUME_ROOT
 from rbac import require_admin
 
 router = APIRouter()
+logger = logging.getLogger(__name__)
 BASE = Path(VOLUME_ROOT)
 
 MAX_UPLOAD_SIZE = 100 * 1024 * 1024  # 100 MB
@@ -131,5 +133,6 @@ def delete(path: str, recursive: bool = False):
     except PermissionError:
         raise HTTPException(status_code=403, detail="Permission denied")
     except OSError as exc:
-        raise HTTPException(status_code=400, detail=str(exc))
+        logger.exception("OS error during file deletion: %s", path)
+        raise HTTPException(status_code=400, detail="Failed to delete file")
     return {"ok": True}