🐛 Add /healthz route to penpot-mcp server

[UsamaSadiq]

Summary

• foss-server-bundle/docker-compose.yml health-checks the penpot-mcp service via curl -f http://localhost:4401/healthz, but the Express app in mcp/packages/server/src/PenpotMcpServer.ts never registered a /healthz route (only /mcp, /sse, and /messages).
• As a result, the container reports Docker health status unhealthy (curl gets a connection/404 failure on /healthz), even though the MCP server itself is running fine.

Fix

• Add a cheap GET /healthz route in setupHttpEndpoints() that returns 200 { "status": "ok" }. It performs no auth checks and pings no downstream dependencies (Penpot API, plugin bridge, Cognito, etc.) — matching the simplicity of other MCP servers' healthz endpoints in this monorepo (e.g. plane-mcp-server's bare-200 /healthz).

Test plan

• make dev.build.penpot.mcp in foss-server-bundle devstack, then confirm docker ps shows the penpot-mcp container as healthy and curl http://localhost:4401/healthz returns 200 {"status":"ok"}.
• No existing test suite/framework exists for mcp/packages/server (no jest config, no test scripts), so no new tests were added, per repo convention of not inventing new test infra for a file that has none.

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