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/opc_agents.py

@@ -2,6 +2,8 @@
 OPC Agents Router
 """
 
+import logging
+
 from fastapi import APIRouter, Depends, HTTPException, Request
 from pydantic import BaseModel
 
@@ -9,6 +11,7 @@ from db import opc_db
 from rbac import User, require_admin
 
 router = APIRouter()
+logger = logging.getLogger(__name__)
 
 
 class AgentUpdate(BaseModel):
@@ -65,7 +68,8 @@ async def update_agent(
         )
         return agent
     except ValueError as e:
-        raise HTTPException(status_code=404, detail=str(e))
+        logger.exception("Failed to update agent %s", agent_id)
+        raise HTTPException(status_code=404, detail="Agent not found")
 
 
 @router.post("/agents/{agent_id}/execute")
@@ -121,4 +125,5 @@ async def approve_execution(
         )
         return execution
     except ValueError as e:
-        raise HTTPException(status_code=404, detail=str(e))
+        logger.exception("Failed to approve agent execution %s", execution_id)
+        raise HTTPException(status_code=404, detail="Execution not found")