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/app/models/api_key.py

@@ -0,0 +1,17 @@
+from datetime import datetime
+
+from sqlalchemy import Boolean, DateTime, String, func
+from sqlalchemy.orm import Mapped, mapped_column
+
+from app.database import Base
+
+
+class ApiKey(Base):
+    __tablename__ = "api_keys"
+
+    id: Mapped[int] = mapped_column(primary_key=True, autoincrement=True)
+    name: Mapped[str] = mapped_column(String(128))
+    key_prefix: Mapped[str] = mapped_column(String(16), index=True)
+    key_hash: Mapped[str] = mapped_column(String(128), unique=True)
+    is_active: Mapped[bool] = mapped_column(Boolean, default=True)
+    created_at: Mapped[datetime] = mapped_column(DateTime(timezone=True), server_default=func.now())