Fix linting issues and update API key test for source validation

- Remove trailing whitespace in auth controller and mobile device model
- Update API key test to expect new validation message with source

🤖 Generated with [Claude Code](https://claude.ai/code)

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

db/schema.rb

@@ -10,7 +10,7 @@
 #
 # It's strongly recommended that you check this file into your version control system.
 
-ActiveRecord::Schema[7.2].define(version: 2025_06_18_110736) do
+ActiveRecord::Schema[7.2].define(version: 2025_06_18_120703) do
   # These are extensions that must be enabled in order to support this database
   enable_extension "pgcrypto"
   enable_extension "plpgsql"
@@ -441,7 +441,9 @@ ActiveRecord::Schema[7.2].define(version: 2025_06_18_110736) do
     t.datetime "last_seen_at"
     t.datetime "created_at", null: false
     t.datetime "updated_at", null: false
+    t.integer "oauth_application_id"
     t.index ["device_id"], name: "index_mobile_devices_on_device_id", unique: true
+    t.index ["oauth_application_id"], name: "index_mobile_devices_on_oauth_application_id"
     t.index ["user_id", "device_id"], name: "index_mobile_devices_on_user_id_and_device_id", unique: true
     t.index ["user_id"], name: "index_mobile_devices_on_user_id"
   end