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/problems/scss/_avatars.scss

@@ -1,77 +0,0 @@
-// Avatars
-.avatar {
-  @include avatar-base();
-  background: $primary-color;
-  border-radius: 50%;
-  color: rgba($light-color, .85);
-  display: inline-block;
-  font-weight: 300;
-  line-height: 1.25;
-  margin: 0;
-  position: relative;
-  vertical-align: middle;
-
-  &.avatar-xs {
-    @include avatar-base($unit-4);
-  }
-  &.avatar-sm {
-    @include avatar-base($unit-6);
-  }
-  &.avatar-lg {
-    @include avatar-base($unit-12);
-  }
-  &.avatar-xl {
-    @include avatar-base($unit-16);
-  }
-
-  img {
-    border-radius: 50%;
-    height: 100%;
-    position: relative;
-    width: 100%;
-    z-index: $zindex-0;
-  }
-
-  .avatar-icon,
-  .avatar-presence {
-    background: $bg-color-light;
-    bottom: 14.64%;
-    height: 50%;
-    padding: $border-width-lg;
-    position: absolute;
-    right: 14.64%;
-    transform: translate(50%, 50%);
-    width: 50%;
-    z-index: $zindex-0 + 1;
-  }
-
-  .avatar-presence {
-    background: $gray-color;
-    box-shadow: 0 0 0 $border-width-lg $light-color;
-    border-radius: 50%;
-    height: .5em;
-    width: .5em;
-
-    &.online {
-      background: $success-color;
-    }
-
-    &.busy {
-      background: $error-color;
-    }
-
-    &.away {
-      background: $warning-color;
-    }
-  }
-
-  &[data-initial]::before {
-    color: currentColor;
-    content: attr(data-initial);
-    left: 50%;
-    position: absolute;
-    top: 50%;
-    transform: translate(-50%, -50%);
-    z-index: $zindex-0;
-  }
-}