feat: impl fs backed blob store

apps/backend/internal/blob/store.go

@@ -0,0 +1,13 @@
+package blob
+
+import (
+	"context"
+	"io"
+)
+
+type Store interface {
+	Put(ctx context.Context, key Key, reader io.Reader) error
+	Retrieve(ctx context.Context, key Key) (io.ReadCloser, error)
+	Delete(ctx context.Context, key Key) error
+	Move(ctx context.Context, srcKey, dstKey Key) error
+}