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/flex-objects/admin/templates/flex-objects.html.twig

@@ -1,30 +0,0 @@
-{%- set user = admin.user -%}
-{%- set route = controller.route -%}
-{%- set type = directory.config('admin.template') ?? target -%}
-
-{# Set action from ?preview=1 #}
-{%- if key and uri.currentUri().queryParam('preview') %}
-    {% set action = 'preview' %}
-{% endif -%}
-
-{%- set template -%}
-    {%- if action == 'add' -%}
-        edit
-    {%- elseif action == 'delete' -%}
-        list
-    {%- else -%}
-        {{- action ?: task ?: 'types' -}}
-    {%- endif -%}
-{%- endset -%}
-
-{%- set separator = config.system.param_sep -%}
-{%- set view_config = directory.config('admin.views.' ~ template) ?? directory.config('admin.' ~ template) ?? [] -%}
-
-{%- include target ? [
-        'flex-objects/types/' ~ type ~ '/' ~ template ~ '.html.twig',
-        'flex-objects/types/default/' ~ template ~ '.html.twig',
-        'flex-objects/layouts/404.html.twig'
-    ] : [
-        'flex-objects/types/default/' ~ template ~ '.html.twig',
-        'flex-objects/layouts/404.html.twig'
-    ] -%}