fix(security): Phase 1 P0 hardening from cross-project audit

Close open uploads, image-proxy SSRF, fail-open AI quotas in production,
auth gaps on app routes, and MCP tenant isolation issues.

Co-authored-by: Cursor <cursoragent@cursor.com>

memento-note/app/actions/semantic-search.ts

@@ -2,7 +2,7 @@
 
 import { semanticSearchService, SearchResult } from '@/lib/ai/services/semantic-search.service'
 import { auth } from '@/auth'
-import { reserveUsageOrThrow, QuotaExceededError } from '@/lib/entitlements'
+import { reserveUsageOrThrow, QuotaExceededError, QuotaServiceUnavailableError } from '@/lib/entitlements'
 
 export interface SemanticSearchResponse {
   results: SearchResult[]
@@ -28,6 +28,11 @@ export async function semanticSearch(
       await reserveUsageOrThrow(session.user.id, 'semantic_search');
     } catch (err) {
       if (err instanceof QuotaExceededError) throw err;
+      if (err instanceof QuotaServiceUnavailableError || process.env.NODE_ENV === 'production') {
+        throw err instanceof QuotaServiceUnavailableError
+          ? err
+          : new QuotaServiceUnavailableError();
+      }
       console.error('[semantic-search] Quota check error (fail-open):', err);
     }
   }