backend: Add a small smoke-test script for local API

[zhuamber370]

What

Add a simple script (Python or shell) that hits a few endpoints to validate a local dev setup.

Example checks:

• GET /health
• GET /api/v1/context/bundle
• GET /api/v1/tasks/views/summary

Where to start

• Put the script under backend/scripts/
• Document usage in docs/contributing/dev-setup.md

Why

Makes it easy for contributors to confirm the backend works without navigating the UI.

Acceptance criteria

• Script lives under backend/scripts/
• Uses only stdlib + existing dependencies
• Clear output and non-zero exit on failure
• Document how to run it

Verification

• With backend running: execute the script and confirm it prints PASS/FAIL per check.

Maintainer support

If you want to take this but are unsure which endpoints are safest to call, comment here and maintainers can propose a minimal set.