feat: add /health endpoint, migrate to lifespan lifecycle, and fix Dockerfile for production

[Arijit429]

Closes #116
Closes #118
Closes #122
Closes #135
Closes #187
Closes #274
Closes #388

Summary

Adds a health check endpoint for container orchestration, migrates database
initialization to FastAPI's modern lifespan pattern, and fixes the Dockerfile
to actually start the application server.

Problem

1. No health check — Docker, Kubernetes, and cloud platforms need a
   /health endpoint to monitor if the app is alive and auto-restart on failure.
   FireForm had no such endpoint.

2. Database init at import time — Template.metadata.create_all() and
   FormSubmission.metadata.create_all() ran at the module top level, meaning
   database tables were created whenever any file imported main.py — including
   during test collection, linting, and static analysis. FastAPI's recommended
   pattern uses lifespan context managers.

3. Dockerfile doesn't start the app — CMD ["tail", "-f", "/dev/null"] keeps
   the container alive but does not run the server. PYTHONPATH was also set to
   /app/src instead of /app, which would break imports.

Changes

api/main.py

• Added GET /health endpoint returning {"status": "healthy", "service": "fireform"}
• Migrated database initialization into lifespan async context manager
• Removed top-level create_all() calls
• Added FastAPI metadata (title, description, version)

Dockerfile

• Changed CMD to start uvicorn server
• Fixed PYTHONPATH from /app/src to /app
• Added EXPOSE 8000
• Added HEALTHCHECK directive using the /health endpoint

Testing

• GET /health returns expected JSON response
• All existing tests pass without modification
• Server startup logs confirm lifespan initialization

Changes Summary

File	Change	Why
api/main.py	Added GET /health endpoint	Docker/K8s liveness probe
api/main.py	Added lifespan context manager	DB init at startup, not import time
api/main.py	Added API metadata (title, description, version)	Professional /docs page
Dockerfile	Changed CMD to uvicorn api.main:app	Old CMD did nothing (tail -f /dev/null)
Dockerfile	Fixed PYTHONPATH /app/src → /app	Imports would fail with old path
Dockerfile	Added HEALTHCHECK directive	Docker auto-restarts unhealthy containers
Dockerfile	Added EXPOSE 8000	Documents container port for platforms

[Arijit429]

Context

Three deployment blockers fixed: added a /health liveness probe for container orchestration, moved database init from import-time to FastAPI's lifespan context manager, and fixed the Dockerfile to actually start the server instead of running tail -f /dev/null.