Add Docker/Lightsail deployment, web search summarization, and fix vite peer dep

- Add backend/frontend Dockerfiles, nginx reverse proxy config, and
  docker-compose.yml to run the app on AWS Lightsail; document the setup
  in docs/deploy-lightsail.md. Fix a .gitignore path anchoring bug that
  left backend/knowledge_base/web_search/ untracked instead of ignored.
- Summarize web search results into structured Markdown via LLM before
  saving them to the local knowledge base, and support regenerating
  existing entries from their source URLs (backend/app/core/memory_kb).
- Downgrade vite to ^6 to match @vitejs/plugin-vue's peer dependency
  range, fixing a failing `npm ci` (found while testing the Docker build).

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

frontend/package.json

@@ -20,7 +20,7 @@
     "@types/dompurify": "^3.0.5",
     "@vitejs/plugin-vue": "^5.0.4",
     "typescript": "^5.4.0",
-    "vite": "^8.0.16",
+    "vite": "^6.0.0",
     "vue-tsc": "^2.0.6"
   }
 }