feat(webui): Enhance dashboard, global styles, and settings module

## Dashboard Enhancements
- Add Request Volume trend chart with Chart.js line graph
  - Support Family/Model display modes for aggregation levels
  - Show Total/Today/1H usage statistics
  - Hierarchical filter dropdown with Smart select (Top 5 by 24h usage)
  - Persist chart preferences to localStorage
- Improve account health detection logic
  - Core models (sonnet/opus/pro/flash) require >5% quota to be healthy
  - Dynamic quota ring chart supporting any model family
- Unify table styles with standard-table class

## Global Style Refactoring
- Add CSS variable system for theming
  - Space color scale (950/900/850/800/border)
  - Neon accent colors (purple/green/cyan/yellow/red)
  - Text hierarchy (main/dim/muted/bright)
  - Chart palette (16 colors)
- Add unified component classes
  - .view-container for consistent page layouts
  - .section-header/.section-title/.section-desc
  - .standard-table for table styling
- Update scrollbar, nav-item, progress-bar to use theme variables

## Settings Module Extensions
- Add model mapping column in Models tab
- Enhance model selectors with family color indicators
- Support horizontal scroll for tabs on narrow screens
- Add defaultCooldownMs and maxWaitBeforeErrorMs config options

## New Module
- Add src/modules/usage-stats.js for request tracking
  - Track /v1/messages and /v1/chat/completions endpoints
  - Hierarchical storage: { hour: { family: { model: count } } }
  - Auto-save every minute, 30-day retention
  - GET /api/stats/history endpoint for dashboard chart

## Backend Changes
- Add direct account manipulation helpers (bypass AccountManager)
- Add POST /api/config/password endpoint for WebUI password change
- Auto-reload AccountManager after account operations
- Use CSS variables in OAuth callback pages

## Other
- Update .gitignore for runtime data directory
- Add i18n keys for new UI elements (EN/zh_CN)

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

public/app.js

@@ -63,8 +63,8 @@ document.addEventListener('alpine:init', () => {
 
             // Chart Defaults
             if (typeof Chart !== 'undefined') {
-                Chart.defaults.color = '#71717a';
-                Chart.defaults.borderColor = '#27272a';
+                Chart.defaults.color = window.utils.getThemeColor('--color-text-dim');
+                Chart.defaults.borderColor = window.utils.getThemeColor('--color-space-border');
                 Chart.defaults.font.family = '"JetBrains Mono", monospace';
             }
 
@@ -111,8 +111,12 @@ document.addEventListener('alpine:init', () => {
 
                     const messageHandler = (event) => {
                         if (event.data?.type === 'oauth-success') {
-                            const action = reAuthEmail ? 're-authenticated' : 'added';
-                            Alpine.store('global').showToast(`Account ${event.data.email} ${action} successfully`, 'success');
+                            const actionKey = reAuthEmail ? 'reauthenticated' : 'added';
+                            const action = Alpine.store('global').t(actionKey);
+                            const successfully = Alpine.store('global').t('successfully');
+                            const msg = `${Alpine.store('global').t('accounts')} ${event.data.email} ${action} ${successfully}`;
+
+                            Alpine.store('global').showToast(msg, 'success');
                             Alpine.store('data').fetchData();
                             document.getElementById('add_account_modal')?.close();
                         }
@@ -120,10 +124,10 @@ document.addEventListener('alpine:init', () => {
                     window.addEventListener('message', messageHandler);
                     setTimeout(() => window.removeEventListener('message', messageHandler), 300000);
                 } else {
-                    Alpine.store('global').showToast(data.error || 'Failed to get auth URL', 'error');
+                    Alpine.store('global').showToast(data.error || Alpine.store('global').t('failedToGetAuthUrl'), 'error');
                 }
             } catch (e) {
-                Alpine.store('global').showToast('Failed to start OAuth flow: ' + e.message, 'error');
+                Alpine.store('global').showToast(Alpine.store('global').t('failedToStartOAuth') + ': ' + e.message, 'error');
             }
         }
     }));