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/Dockerfile

@@ -0,0 +1,21 @@
+FROM python:3.12-slim-bookworm
+
+WORKDIR /app
+
+RUN apt-get update && apt-get install -y --no-install-recommends libpq5 \
+    && rm -rf /var/lib/apt/lists/*
+
+COPY backend/requirements.txt .
+RUN pip install --no-cache-dir -r requirements.txt
+
+COPY backend/app ./app
+COPY backend/alembic.ini .
+COPY backend/alembic ./alembic
+COPY schemas ./schemas
+
+ENV PYTHONPATH=/app
+ENV PYTHONUNBUFFERED=1
+ENV EVENT_SCHEMA_PATH=/app/schemas/event-schema-v1.json
+
+EXPOSE 8000
+CMD ["uvicorn", "app.main:app", "--host", "0.0.0.0", "--port", "8000"]