Move plugins to manifest, pin Docker version, add Makefile

- Add plugins.txt listing all plugins for reproducible installs
- Add Makefile with setup/start/stop/install-plugins targets
- Remove user/plugins/ from git tracking
- Pin Docker image to 1.7.49.5-ls244

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

plugins/admin/themes/grav/app/forms/index.js

@@ -1,16 +0,0 @@
-import FormState, { Instance as FormStateInstance } from './state';
-import Form, { Instance as FormInstance } from './form';
-
-import Fields from './fields';
-
-export default {
-    Form: {
-        Form,
-        Instance: FormInstance
-    },
-    Fields,
-    FormState: {
-        FormState,
-        Instance: FormStateInstance
-    }
-};