Generate a presigned GET URL for an S3 object 🟩

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

infrastructure/s3/s3_client.py

@@ -25,4 +25,9 @@ class S3Client:
         """A time-limited URL that lets the holder GET this object without AWS
         credentials (ADR-0060 — how a Download Package link is delivered).
         ``expires_in`` is the validity window in seconds."""
-        raise NotImplementedError
+        url: str = self._client.generate_presigned_url(
+            "get_object",
+            Params={"Bucket": self._bucket, "Key": key},
+            ExpiresIn=expires_in,
+        )
+        return url