Add local-first SPA architecture and containerized production deploy.

Move data access to use-cases and IndexedDB repositories with optional
remote fallback, changelog/sync ports, and encrypted local backup.
Add production Docker Compose (nginx frontend + optional backend) and
Apache host proxy configuration for deployment.

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

frontend/package.json

@@ -14,6 +14,7 @@
     "vue-router": "^4.3.0",
     "pinia": "^2.1.7",
     "axios": "^1.6.7",
+    "dexie": "^4.2.1",
     "vis-network": "^9.1.9",
     "vis-data": "^7.1.9"
   },