feat: multipart blob sync support (#14138)

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-->
## Summary by CodeRabbit

* **New Features**
* Flexible blob uploads: GRAPHQL, presigned, and multipart flows with
per‑part URLs, abort/complete operations, presigned proxy endpoints, and
nightly cleanup of expired pending uploads.

* **API / Schema**
* GraphQL additions: new types, mutations, enum and error to manage
upload lifecycle (create, complete, abort, get part URL).

* **Database**
* New blob status enum and columns (status, upload_id); listing now
defaults to completed blobs.

* **Localization**
  * Added user-facing message: "Blob is invalid."

* **Tests**
* Expanded unit and end‑to‑end coverage for upload flows, proxy
behavior, multipart and provider integrations.

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<!-- end of auto-generated comment: release notes by coderabbit.ai -->

packages/backend/server/migrations/20251222184223_add_blob_status/migration.sql

@@ -0,0 +1,6 @@
+-- CreateEnum
+CREATE TYPE "BlobStatus" AS ENUM ('pending', 'completed');
+
+-- AlterTable
+ALTER TABLE "blobs" ADD COLUMN     "status" "BlobStatus" NOT NULL DEFAULT 'completed',
+ADD COLUMN     "upload_id" VARCHAR;