fix: address Phase 2 COE verification findings — dropdown styling, ARIA, sidebar clipping, manage-views wiring, persistence

Fix 1: BEM class names — renderViewDropdown/renderSidebarViewDropdown now emit
view-dropdown__item, __separator, __shortcut, __action, __count matching CSS

Fix 2: role=menuitem — all buttons in both dropdown renderers now carry
role="menuitem" so handleGlobalKeydown arrow-key navigation works

Fix 3: Sidebar dropdown clipping — #sidebar-view-dropdown-menu changed to
position:fixed; toggleSidebarViewDropdown uses getBoundingClientRect() to
escape .session-sidebar { overflow:hidden } clipping

Fix 4: manage-views wiring — bindStaticEventListeners now calls
openSettings() + switchSettingsTab('views') instead of falling through to
closeViewDropdown only

Fix 5: active_view persistence — delete and rename paths in
renderViewsSettingsTab now PATCH /api/state when _activeView changes

Fix 6: Sidebar dropdown click-outside — second document click listener
closes sidebar-view-dropdown-menu on outside clicks

Fix 7: Case-insensitive reserved names — showNewViewInput and commitRename
use name.toLowerCase() for 'all'/'hidden' check

Fix 8: Rename input maxLength — views-settings-rename-input now has
maxLength=30 matching the creation input

Fix 9: Local device_id — added _localDeviceId variable, fetched from
/api/instance-info at startup; createNewSession uses _localDeviceId instead
of _serverSettings.device_id (which is not in /api/settings response)

Fix 10: Dead code — renderFilterBar body emptied; dead filter-bar click
handler removed from bindStaticEventListeners

Tests: 24 new tests added covering all 10 findings; 1070 total tests pass

muxplex/frontend/style.css

@@ -517,8 +517,7 @@ body {
 }
 
 #sidebar-view-dropdown-menu {
-  left: 0;
-  top: calc(100% + 2px);
+  position: fixed;
   min-width: 180px;
 }