Phase 3: Fix medium-priority issues (M1-M4, M6)

M1: Password complexity validation (min 8 chars, uppercase, lowercase, digit)
M2: Remove is_system_admin from login response (prevent role leaking)
M3: Permission cache invalidates on DB error instead of using stale data
M4: .env.docker.example already fixed in B9 (SECRET_KEY, FRONTEND_URL, SMTP)
M6: Frontend test setup auto-wraps with QueryClientProvider (fixes ~29 test failures)

Remaining: M5 (frontend component integration — WelcomeDialog, SavedFilterBar, etc.)

app/core/permissions.py

@@ -337,11 +337,13 @@ async def get_cached_permissions(
         except Exception:
             logger.warning(
                 "Failed to query current permission_version for cache validation "
-                "(user=%s, tenant=%s) — using cached data",
+                "(user=%s, tenant=%s) — invalidating cache and re-resolving",
                 user_id, tenant_id,
                 exc_info=True,
             )
-            current_version = cached_version  # assume cache is valid if we can't check
+            # Invalidate stale cache — do NOT trust cached permissions on DB error
+            await redis.delete(cache_key)
+            return None  # Fall through to re-resolution from DB
 
         if cached_version == current_version:
             return data