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-replace/blueprints/media-replace.yaml

@@ -1,51 +0,0 @@
-form:
-  fields:
-  
-    foobar:
-      type: section
-      title: Replace Media
-    
-    rename_file:
-      type: toggle
-      label: Rename file
-      description: Renames the uploaded file to the target file name.  This includes the basename and extension.
-      highlight: 1
-      default: 1
-      options:
-        1: Yes
-        0: No
-      validate:
-        type: bool
-
-    require_image:
-      type: toggle
-      label: Require image
-      description: Require upload to be an image MIME type.
-      highlight: 0
-      default: 0
-      options:
-        1: Yes
-        0: No
-      validate:
-        type: bool
-
-    match_extension:
-      type: toggle
-      label: Match Extension
-      description: Require new file extension to match current file extension.
-      highlight: 0
-      default: 0
-      options:
-        1: Yes
-        0: No
-      validate:
-        type: bool
-                
-    file:
-      type: singlefile
-      label: File
-      description: You can also drop a file on the <em>choose file button</em>.
-
-    spacer:
-      type: spacer
-      text: To bypass this dialog and simply <em>pick and send</em> the file using default values, go to the plugin settings and enable <em>quicksend</em>.