feat: add Views settings tab with inline rename, reorder, and delete

Implements the "Manage Views" Settings Tab with full UI and functionality:

HTML: Added Views tab button and panel with empty state message.
JS: Added renderViewsSettingsTab() function that renders the view list with:
- Clickable name for inline rename (validates reserved/duplicate names)
- Session count display
- Up/down arrow buttons for reordering (disabled at boundaries)
- Delete button with inline 'Sure? [Yes] [No]' confirmation
- Delegated event handlers for all interactions
Added _saveViewsAndRerender() helper that PATCHes /api/settings,
updates _serverSettings, and re-renders both tab and dropdown.
Updated openSettings() to call renderViewsSettingsTab() after loading.
CSS: Added styling for views-settings-list, views-settings-row,
views-settings-name, views-settings-count, views-settings-actions,
views-settings-btn, views-settings-confirm, and rename input.
Tests: Added 3 new frontend tests and updated existing panel count test.

All 491 frontend tests pass with no regressions.

Generated with Amplifier

Co-Authored-By: Amplifier <240397093+microsoft-amplifier@users.noreply.github.com>

muxplex/frontend/style.css

@@ -2001,3 +2001,99 @@ body {
   border-radius: 4px;
   color: var(--text);
 }
+
+/* ─── Manage Views settings tab (task-9) ─────────────────────────────────── */
+
+.views-settings-list {
+  display: flex;
+  flex-direction: column;
+  gap: 4px;
+  width: 100%;
+}
+
+.views-settings-row {
+  display: flex;
+  align-items: center;
+  gap: 8px;
+  padding: 6px 8px;
+  background: var(--bg-secondary);
+  border: 1px solid var(--border);
+  border-radius: 4px;
+}
+
+.views-settings-name {
+  flex: 1;
+  font-size: 13px;
+  color: var(--text);
+  cursor: pointer;
+  overflow: hidden;
+  text-overflow: ellipsis;
+  white-space: nowrap;
+}
+
+.views-settings-name:hover {
+  color: var(--accent);
+  text-decoration: underline;
+}
+
+.views-settings-count {
+  font-size: 11px;
+  color: var(--text-muted);
+  white-space: nowrap;
+  flex-shrink: 0;
+}
+
+.views-settings-actions {
+  display: flex;
+  align-items: center;
+  gap: 4px;
+  flex-shrink: 0;
+}
+
+.views-settings-btn {
+  background: transparent;
+  border: 1px solid var(--border);
+  border-radius: 4px;
+  color: var(--text-muted);
+  cursor: pointer;
+  font-size: 12px;
+  line-height: 1;
+  padding: 3px 7px;
+  transition: color 0.15s, border-color 0.15s, background 0.15s;
+}
+
+.views-settings-btn:hover:not(:disabled) {
+  border-color: var(--accent);
+  color: var(--accent);
+  background: var(--accent-dim);
+}
+
+.views-settings-btn:disabled {
+  opacity: 0.35;
+  cursor: not-allowed;
+}
+
+.views-settings-btn--danger:hover:not(:disabled) {
+  border-color: #ef4444;
+  color: #ef4444;
+  background: rgba(239, 68, 68, 0.1);
+}
+
+.views-settings-confirm {
+  display: inline-flex;
+  align-items: center;
+  gap: 4px;
+  font-size: 12px;
+  color: var(--text-muted);
+}
+
+.views-settings-rename-input {
+  flex: 1;
+  background: var(--bg);
+  border: 1px solid var(--accent);
+  border-radius: 4px;
+  color: var(--text);
+  font-size: 13px;
+  padding: 3px 6px;
+  outline: none;
+}