bootstrap removal phase 4b: hand-rolled list-group (drop list-group)

Replaced bootstrap/list-group with the used base only (.list-group,
.list-group-item, .list-group-horizontal + first/last-child radii). Resolved
values hardcoded (body-bg #d3d3d3 = the gray rows, border #dee2e6, color
#232323). Context overrides (ul.nav, .list-group-horizontal, #music) already
in style.css. Verified analytics lists unchanged.
v4-style.min.css 114,398 -> 104,763 bytes.

css/styles.scss

@@ -76,7 +76,6 @@ $enable-negative-margins: true;
 @import '../node_modules/bootstrap/scss/nav';
 @import '../node_modules/bootstrap/scss/navbar';
 @import '../node_modules/bootstrap/scss/card';
-@import '../node_modules/bootstrap/scss/list-group';
 
 // ---- replacements for dropped Bootstrap partials (Phase 1 + 2) ----
 
@@ -222,6 +221,33 @@ $dw-cols: 8.333333%, 16.666667%, 25%, 33.333333%, 41.666667%, 50%, 58.333333%, 6
 @media (min-width: 768px) { .offset-md-1 { margin-left: 8.333333%; } }
 @media (min-width: 992px) { .offset-lg-1 { margin-left: 8.333333%; } }
 
+// ---- list-group (hand-rolled; replaces bootstrap/list-group) ----
+// Base only; context overrides (ul.nav, .list-group-horizontal, #music) live in
+// style.css. Resolved values: body-color #232323, body-bg #d3d3d3 (the gray
+// rows on music/analytics), border #dee2e6, radius .375rem.
+.list-group {
+  display: flex;
+  flex-direction: column;
+  padding-left: 0;
+  margin-bottom: 0;
+  border-radius: 0.375rem;
+}
+.list-group-item {
+  position: relative;
+  display: block;
+  padding: 0.5rem 1rem;
+  color: #232323;
+  background-color: #d3d3d3;
+  border: 1px solid #dee2e6;
+  text-decoration: none;
+}
+.list-group-item:first-child { border-top-left-radius: inherit; border-top-right-radius: inherit; }
+.list-group-item:last-child { border-bottom-left-radius: inherit; border-bottom-right-radius: inherit; }
+.list-group-item + .list-group-item { border-top-width: 0; }
+.list-group-horizontal { flex-direction: row; }
+.list-group-horizontal > .list-group-item:first-child:not(:last-child) { border-bottom-left-radius: 0.375rem; border-top-right-radius: 0; }
+.list-group-horizontal > .list-group-item:last-child:not(:first-child) { border-bottom-left-radius: 0; border-top-right-radius: 0.375rem; }
+
 /* Bootstrap Icons font dropped (2026-06-19): the header's 8 nav icons are now
    inline SVG in parts/header.html, so the full icon font + its ~2000 CSS rules
    are no longer imported. */