add sqlc, fix background img fetching

grpc-backend/sqlc.yaml

@@ -0,0 +1,14 @@
+version: "2"
+sql:
+  - engine: "sqlite"
+    schema: "sqlc/schema"
+    queries: "sqlc/query"
+    database:
+      uri: "file:data/music.db"
+    gen:
+      go:
+        package: "db"
+        out: "internal/db"
+        emit_json_tags: true
+        emit_interface: true
+        emit_empty_slices: true