Add media (object storage) and the background worker (Phase 1)

Media model + migration; an ObjectStore interface with an S3/MinIO (boto3) implementation behind the service layer. Upload (multipart) stores bytes in object storage + a metadata row (checksum, size, content-type, optional attach to person/event/source); list returns presigned URLs; delete is soft. Editor-gated, privacy-filtered, audited. 24 tests pass (object store faked).

Introduces the worker container (same image, 'python -m app.worker'): its first job is the scheduled 30-day soft-delete purge across tables + media object cleanup. Compose gains worker + S3 env on backend/worker; dev override builds the worker too.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Signed-off-by: Justin Paul <justin@jpaul.me>

backend/app/api/deps.py

@@ -10,6 +10,8 @@ from app.core.db import get_session
 from app.integrations.mailer.base import Mailer
 from app.integrations.mailer.console import ConsoleMailer
 from app.integrations.mailer.smtp import SMTPMailer
+from app.integrations.objectstore.base import ObjectStore
+from app.integrations.objectstore.s3 import S3ObjectStore
 from app.models.user import User
 from app.services import auth_service
 
@@ -46,3 +48,10 @@ def get_mailer() -> Mailer:
 
 
 MailerDep = Annotated[Mailer, Depends(get_mailer)]
+
+
+def get_objectstore() -> ObjectStore:
+    return S3ObjectStore(get_settings())
+
+
+ObjectStoreDep = Annotated[ObjectStore, Depends(get_objectstore)]