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/services/schema_validate.py

@@ -0,0 +1,24 @@
+import json
+from functools import lru_cache
+from pathlib import Path
+
+import jsonschema
+from jsonschema import Draft202012Validator
+
+from app.config import get_settings
+
+
+@lru_cache
+def get_event_validator() -> Draft202012Validator:
+    path = Path(get_settings().event_schema_path)
+    if not path.is_file():
+        path = Path(__file__).resolve().parents[3] / "schemas" / "event-schema-v1.json"
+    schema = json.loads(path.read_text(encoding="utf-8"))
+    Draft202012Validator.check_schema(schema)
+    return Draft202012Validator(schema)
+
+
+def validate_event_payload(payload: dict) -> list[str]:
+    validator = get_event_validator()
+    errors = sorted(validator.iter_errors(payload), key=lambda e: e.path)
+    return [e.message for e in errors]