feat: add stdio runner and bridge sidecar

[vamgan]

Summary

• add a runnable stdio entrypoint for @askable-ui/mcp
• add a local HTTP bridge sidecar for ingesting askable snapshots and draining queued select_element commands
• document Claude Desktop setup plus a browser/app bridge example

Test Plan

• npm test
• npm run build
• node dist/cli.js --bridge-port 4418 then verify GET /health and POST /bridge / GET /sessions