feat: Add context7-mcp with custom Dockerfile

- Create dockerfiles/context7/Dockerfile for monorepo build
- Update docker-compose.yml to use custom Dockerfile context
- Build approach: copy all source, then pnpm install workspaces, then build:mcp
- Requires UPSTASH_REDIS_REST_URL and UPSTASH_REDIS_REST_TOKEN env vars
- Follows AGENTS.md guidelines for Dockerfile management

Note: Monorepo structure requires full source copy before dependency resolution
to properly install workspace dependencies across packages/mcp, packages/sdk, etc.

dockerfiles/context7/Dockerfile

@@ -0,0 +1,19 @@
+FROM node:22-alpine
+
+# Install pnpm for monorepo
+RUN npm install -g pnpm
+
+WORKDIR /app
+
+# Copy all source first
+COPY . .
+
+# Install all workspace dependencies (from within source tree)
+RUN pnpm install
+
+# Build MCP package specifically
+RUN pnpm build:mcp
+
+# Set entrypoint to run MCP server
+ENTRYPOINT ["node", "packages/mcp/dist/index.js"]
+CMD ["--transport", "stdio"]