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/_tables.scss

@@ -1,57 +0,0 @@
-// Tables
-.table {
-  border-collapse: collapse;
-  border-spacing: 0;
-  width: 100%;
-  @if $rtl == true {
-    text-align: right;
-  } @else {
-    text-align: left;
-  }
-
-  &.table-striped {
-    tbody {
-      tr:nth-of-type(odd) {
-        background: $bg-color;
-      }
-    }
-  }
-
-  &,
-  &.table-striped {
-    tbody {
-      tr {
-        &.active {
-          background: $bg-color-dark;
-        }
-      }
-    }
-  }
-
-  &.table-hover {
-    tbody {
-      tr {
-        &:hover {
-          background: $bg-color-dark;
-        }
-      }
-    }
-  }
-
-  // Tables with horizontal scrollbar
-  &.table-scroll {
-    display: block;
-    overflow-x: auto;
-    padding-bottom: .75rem;
-    white-space: nowrap;
-  }
-
-  td,
-  th {
-    border-bottom: $border-width solid $border-color;
-    padding: $unit-3 $unit-2;
-  }
-  th {
-    border-bottom-width: $border-width-lg;
-  }
-}