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/auth/api_key.py

@@ -0,0 +1,40 @@
+import hashlib
+import secrets
+
+from fastapi import Depends, HTTPException, Security
+from fastapi.security import HTTPAuthorizationCredentials, HTTPBearer
+from sqlalchemy import select
+from sqlalchemy.orm import Session
+
+from app.database import get_db
+from app.models import ApiKey
+
+security_scheme = HTTPBearer(auto_error=False)
+
+
+def hash_api_key(raw_key: str) -> str:
+    return hashlib.sha256(raw_key.encode("utf-8")).hexdigest()
+
+
+def generate_api_key() -> tuple[str, str, str]:
+    """Returns (full_key, prefix, hash)."""
+    raw = f"sac_{secrets.token_urlsafe(32)}"
+    prefix = raw[:12]
+    return raw, prefix, hash_api_key(raw)
+
+
+def verify_api_key(db: Session, raw_key: str) -> bool:
+    key_hash = hash_api_key(raw_key)
+    row = db.scalar(select(ApiKey).where(ApiKey.key_hash == key_hash, ApiKey.is_active.is_(True)))
+    return row is not None
+
+
+def get_api_key_auth(
+    credentials: HTTPAuthorizationCredentials | None = Security(security_scheme),
+    db: Session = Depends(get_db),
+) -> str:
+    if credentials is None or credentials.scheme.lower() != "bearer":
+        raise HTTPException(status_code=401, detail="Missing or invalid Authorization header")
+    if not verify_api_key(db, credentials.credentials):
+        raise HTTPException(status_code=401, detail="Invalid API key")
+    return credentials.credentials