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>

backend/Dockerfile

@@ -0,0 +1,22 @@
+FROM python:3.12-slim
+
+RUN pip install --no-cache-dir uv
+
+WORKDIR /app
+
+ENV UV_COMPILE_BYTECODE=1 \
+    UV_LINK_MODE=copy \
+    PYTHONUNBUFFERED=1
+
+# 依存関係だけ先にインストールしてレイヤーキャッシュを効かせる
+COPY pyproject.toml uv.lock ./
+RUN uv sync --frozen --no-install-project --no-dev
+
+COPY . .
+RUN uv sync --frozen --no-dev
+
+ENV PATH="/app/.venv/bin:$PATH"
+
+EXPOSE 8000
+
+CMD ["uvicorn", "app.main:app", "--host", "0.0.0.0", "--port", "8000"]