FastAPI for run management

[Headonpillow]

Create minimal FastAPI app exposing POST /runs (start run), GET /runs (list metadata), GET /runs/{id} (status/log links).

Why? - This is needed as a backend to control what happens inside the container from an outside browser.

• Wire it to run_pipeline.py and run.json files; serve static logs.
• Add an entrypoint script uvicorn app:app --host 0.0.0.0 --port 8000.

Acceptance criteria:

• curl can start a run and list statuses.