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/codeception.yml

@@ -1,18 +0,0 @@
-actor: Tester
-paths:
-    tests: tests
-    log: tests/_output
-    data: tests/_data
-    support: tests/_support
-    envs: tests/_envs
-settings:
-    bootstrap: _bootstrap.php
-    colors: true
-    memory_limit: 1024M
-extensions:
-    enabled:
-        - Codeception\Extension\RunFailed
-        # - Codeception\Extension\Recorder
-
-modules:
-    config: