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>

deploy/docker-compose.dev.yml

@@ -12,6 +12,11 @@ services:
       context: ../backend
       dockerfile: Dockerfile
 
+  worker:
+    build:
+      context: ../backend
+      dockerfile: Dockerfile
+
   frontend:
     build:
       context: ../frontend

deploy/docker-compose.yml

@@ -47,9 +47,16 @@ services:
     environment:
       APP_ENV: ${APP_ENV:-development}
       DATABASE_URL: ${DATABASE_URL:-postgresql+asyncpg://provenance:provenance@postgres:5432/provenance}
+      S3_ENDPOINT_URL: ${S3_ENDPOINT_URL:-http://minio:9000}
+      S3_BUCKET: ${S3_BUCKET:-provenance}
+      S3_ACCESS_KEY: ${S3_ACCESS_KEY:-provenance}
+      S3_SECRET_KEY: ${S3_SECRET_KEY:-change-me-too}
+      S3_REGION: ${S3_REGION:-us-east-1}
     depends_on:
       postgres:
         condition: service_healthy
+      minio:
+        condition: service_healthy
     healthcheck:
       test:
         - CMD-SHELL
@@ -62,6 +69,28 @@ services:
       start_period: 20s
     restart: unless-stopped
 
+  # Background worker — same image as the backend, run in worker mode.
+  # First job: the scheduled soft-delete purge (and media object cleanup).
+  worker:
+    image: git.jpaul.io/justin/provenance-backend:${IMAGE_TAG:-test-main}
+    command: ["uv", "run", "--no-dev", "python", "-m", "app.worker"]
+    labels:
+      com.centurylinklabs.watchtower.enable: "true"
+    environment:
+      APP_ENV: ${APP_ENV:-development}
+      DATABASE_URL: ${DATABASE_URL:-postgresql+asyncpg://provenance:provenance@postgres:5432/provenance}
+      S3_ENDPOINT_URL: ${S3_ENDPOINT_URL:-http://minio:9000}
+      S3_BUCKET: ${S3_BUCKET:-provenance}
+      S3_ACCESS_KEY: ${S3_ACCESS_KEY:-provenance}
+      S3_SECRET_KEY: ${S3_SECRET_KEY:-change-me-too}
+      S3_REGION: ${S3_REGION:-us-east-1}
+    depends_on:
+      postgres:
+        condition: service_healthy
+      minio:
+        condition: service_healthy
+    restart: unless-stopped
+
   frontend:
     image: git.jpaul.io/justin/provenance-frontend:${IMAGE_TAG:-test-main}
     labels: