Redesign admin sidebar: collapsible categories, icons, role-accurate nav

Regroup the flat 12-link staff sidebar into collapsible category sections
(Content / Moderation / System, with Dashboard and Account ungrouped) and
add a small inline-SVG icon per item. Category collapse state persists in
localStorage and the group holding the active route auto-opens.

Gate each item by role to match server-side enforcement so the sidebar no
longer shows links that would 403: Content is admin/editor, Moderation is
admin/moderator, System (Users, Settings, Hero Editor, Authentication,
Discord Bot, Web Bot Activity) is admin-only. Existing moderator confinement
(Moderation + Account only, plus redirect) is preserved.

Rename "Bot Activity" to "Web Bot Activity" to distinguish the bot-scoring
view from the Discord Bot.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

client/src/styles/theme.css

@@ -688,6 +688,47 @@ button[disabled] {
     grid-template-columns: 1fr;
   }
 }
+/* Admin sidebar — collapsible category sections */
+.admin-nav-group {
+  display: flex;
+  flex-direction: column;
+  gap: 4px;
+  margin-top: 6px;
+}
+.admin-nav-head {
+  display: flex;
+  align-items: center;
+  justify-content: space-between;
+  width: 100%;
+  padding: 6px 14px 4px;
+  border: 0;
+  background: transparent;
+  color: var(--dim);
+  font-size: 0.66rem;
+  letter-spacing: 0.14em;
+  text-transform: uppercase;
+  cursor: pointer;
+  transition: color 0.15s;
+}
+.admin-nav-head:hover {
+  color: var(--muted);
+}
+.admin-nav-chev {
+  transition: transform 0.15s ease;
+  flex: 0 0 auto;
+}
+.admin-nav-items {
+  padding-left: 6px;
+}
+.admin-nav-link > span {
+  min-width: 0;
+  overflow: hidden;
+  text-overflow: ellipsis;
+  white-space: nowrap;
+}
+.admin-nav-link svg {
+  flex: 0 0 16px;
+}
 .wiki-grid {
   display: grid;
   grid-template-columns: 230px 1fr;