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-media-actions/CHANGELOG.md

@@ -1,32 +0,0 @@
-# v1.0.4
-## 2/15/2018
-
-1. [](#new)
-    * Update styles for Grav Admin v1.7.
-
-# v1.0.3
-## 2/15/2018
-
-1. [](#new)
-    * Add column margin to media actions.
-    * Add border-radius to media actions.
-    
-# v1.0.2
-## 2/14/2018
-
-1. [](#new)
-    * Update bugs URL.
-    * Update addAction signature
-
-# v1.0.1
-## 2/7/2018
-
-1. [](#new)
-    * Show alert dialog for sample actions.
-    * Update sample action log message.
-
-# v1.0.0
-##  1/24/2018
-
-1. [](#Initial)
-    *