feat(db): change to sqlc Querier in Store

this generates an interface for our sqlc methods and
changes the db Store to hold that instead in preparation
for mocking and integration tests

sqlc.yaml

@@ -14,6 +14,7 @@ sql:
         emit_json_tags: true
         emit_pointers_for_null_types: true
         emit_empty_slices: true
+        emit_interface: true
         overrides:
           - db_type: "uuid"
             go_type: "github.com/google/uuid.UUID"