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/tests/test_media.py

@@ -0,0 +1,45 @@
+"""Media upload/list/delete through the API (object store faked in conftest)."""
+
+from tests.conftest import auth, register
+
+
+async def _tree(client, email):
+    h = auth(await register(client, email))
+    tree_id = (await client.post("/api/v1/trees", json={"name": "M"}, headers=h)).json()["id"]
+    return h, tree_id
+
+
+async def test_media_upload_list_delete(client):
+    h, tree_id = await _tree(client, "media1@example.com")
+
+    resp = await client.post(
+        f"/api/v1/trees/{tree_id}/media",
+        files={"file": ("scan.txt", b"hello world", "text/plain")},
+        data={"title": "A scan"},
+        headers=h,
+    )
+    assert resp.status_code == 201, resp.text
+    body = resp.json()
+    assert body["original_filename"] == "scan.txt"
+    assert body["byte_size"] == 11
+    assert body["url"].startswith("https://objects.test/")
+    media_id = body["id"]
+
+    listed = await client.get(f"/api/v1/trees/{tree_id}/media", headers=h)
+    assert listed.status_code == 200
+    assert len(listed.json()) == 1
+
+    resp = await client.delete(f"/api/v1/trees/{tree_id}/media/{media_id}", headers=h)
+    assert resp.status_code == 204
+    assert len((await client.get(f"/api/v1/trees/{tree_id}/media", headers=h)).json()) == 0
+
+
+async def test_non_member_cannot_upload(client):
+    h, tree_id = await _tree(client, "media2@example.com")
+    other = auth(await register(client, "media-intruder@example.com"))
+    resp = await client.post(
+        f"/api/v1/trees/{tree_id}/media",
+        files={"file": ("x.txt", b"x", "text/plain")},
+        headers=other,
+    )
+    assert resp.status_code == 403