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/scss/configuration/template/_variables.scss

@@ -1,22 +0,0 @@
-// Sizes
-$header-height: 5rem;
-$footer-height: 6rem;
-$border-radius: 4px;
-
-// Font Weights
-$font-weight-bold: 600;
-$font-weight-regular: 400;
-$font-weight-light:300;
-
-// Global Paddings
-$padding-default: 1.5rem;
-$padding-horiz: 7rem;
-$padding-vert: 3rem;
-
-//Forms
-$form-label-width: 30%;
-$form-border-radius: 4px;
-$form-border-width: 1px;
-$form-label-pad: 5px 0 5px 3rem;
-$form-input-pad: 5px 10px;
-$form-select-pad: 5px 30px 5px 10px;