feat: backend ingest API, Docker Compose, Ubuntu install guide

- FastAPI: POST /api/v1/events, GET /health, JSON Schema validation

- PostgreSQL models, Alembic migration, bootstrap API key

- deploy/docker-compose.yml, .env.example

- docs/install-ubuntu-24.04.md, updated work-plan (agents first)

backend/tests/test_health.py

@@ -0,0 +1,7 @@
+"""Smoke tests — run with PostgreSQL or skip integration."""
+
+import pytest
+
+
+def test_placeholder():
+    assert True