feat: generate OpenAPI spec without a running server

[gunhileb]

Why is this pull request needed?

This pull request is needed because generating the TypeScript API client currently requires a running API server on localhost:5000.

What does this pull request change?

• Adds an open-api CLI command to app.py that generates the OpenAPI spec by instantiating the FastAPI app directly in Python — no server required.
• The pre-commit hook and package.json generate script are updated to use this command (uv run python -m app open-api) instead of fetching the spec via curl from a live server.

Issues related to this change:

Close #394