Stream media through the backend (browser-reachable, privacy-checked)

Presigned URLs point at the internal minio:9000 host a browser can't reach. Add ObjectStore.get_object and a GET /media/{id}/content endpoint that resolves visibility and streams the bytes; MediaRead.url now points there. Keeps the object store private and downloads behind the privacy engine.

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

backend/app/integrations/objectstore/s3.py

@@ -44,6 +44,13 @@ class S3ObjectStore(ObjectStore):
             ContentType=content_type,
         )
 
+    async def get_object(self, *, key: str) -> bytes:
+        def _get() -> bytes:
+            obj = self._client.get_object(Bucket=self.bucket, Key=key)
+            return obj["Body"].read()
+
+        return await asyncio.to_thread(_get)
+
     async def presigned_get_url(self, *, key: str) -> str:
         return await asyncio.to_thread(
             self._client.generate_presigned_url,