feat(webui): Add Models tab and refactor model configuration

- Add standalone Models tab with real-time quota/status display
- Move model identity table from Dashboard to Models tab
- Slim down Dashboard to KPI cards and charts only
- Dashboard charts now use unfiltered data (independent of Models filters)

Settings > Models improvements:
- Remove redundant Alias column (only Mapping is functional)
- Fix column misalignment bug (empty td)
- Add column widths and hidden row opacity styling
- Single row edit constraint (only one Mapping editable at a time)
- showHiddenModels toggle now only affects Settings (not Models tab)
- Update description text to match current functionality

i18n:
- Add 'models' and 'modelsPageDesc' keys (EN/ZH)
- Add 'modelMappingHint' for Claude CLI guidance
- Update 'modelsDesc' to reflect new functionality

public/app.js

@@ -9,6 +9,7 @@
 document.addEventListener('alpine:init', () => {
     // Register Components (loaded from separate files via window.Components)
     Alpine.data('dashboard', window.Components.dashboard);
+    Alpine.data('models', window.Components.models);
     Alpine.data('accountManager', window.Components.accountManager);
     Alpine.data('claudeConfig', window.Components.claudeConfig);
     Alpine.data('logsViewer', window.Components.logsViewer);