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/js/components/model-manager.js

@@ -6,10 +6,36 @@
 window.Components = window.Components || {};
 
 window.Components.modelManager = () => ({
+    // Track which model is currently being edited (null = none)
+    editingModelId: null,
+
     init() {
         // Component is ready
     },
 
+    /**
+     * Start editing a model's mapping
+     * @param {string} modelId - The model to edit
+     */
+    startEditing(modelId) {
+        this.editingModelId = modelId;
+    },
+
+    /**
+     * Stop editing
+     */
+    stopEditing() {
+        this.editingModelId = null;
+    },
+
+    /**
+     * Check if a model is being edited
+     * @param {string} modelId - The model to check
+     */
+    isEditing(modelId) {
+        return this.editingModelId === modelId;
+    },
+
     /**
      * Update model configuration with authentication
      * @param {string} modelId - The model ID to update