feat: Add Web UI for account and quota management

## Summary
Add an optional Web UI for managing accounts and monitoring quotas.
WebUI is implemented as a modular plugin with minimal changes to server.js (only 5 lines added).

## New Features
- Dashboard: Real-time model quota visualization with Chart.js
- Accounts: OAuth-based account management (add/enable/disable/refresh/remove)
- Logs: Live server log streaming via SSE with search and level filtering
- Settings: System configuration with 4 tabs
  - Interface: Language (EN/zh_CN), polling interval, log buffer size, display options
  - Claude CLI: Proxy connection config, model selection, alias overrides (~/.claude.json)
  - Models: Model visibility and ordering management
  - Server Info: Runtime info and account config reload

## Technical Changes
- Add src/webui/index.js as modular plugin (all WebUI routes encapsulated)
- Add src/config.js for centralized configuration (~/.config/antigravity-proxy/config.json)
- Add authMiddleware for optional password protection (WEBUI_PASSWORD env var)
- Enhance logger with EventEmitter for SSE log streaming
- Make constants configurable via config.json
- Merge with main v1.2.6 (model fallback, cross-model thinking)
- server.js changes: only 5 lines added to import and mount WebUI module

## Bug Fixes
- Fix Alpine.js $watch error in settings-store.js (not supported in store init)
- Fix "OK" label to "SUCCESS" in logs filter
- Add saveSettings() calls to settings toggles for proper persistence
- Improve Claude CLI config robustness (handle empty/invalid JSON files)
- Add safety check for empty config.env in claude-config component
- Improve config.example.json instructions with clear Windows/macOS/Linux paths

## New Files
- src/webui/index.js - WebUI module with all API routes
- public/ - Complete Web UI frontend (Alpine.js + TailwindCSS + DaisyUI)
- src/config.js - Configuration management
- src/utils/claude-config.js - Claude CLI settings helper
- tests/frontend/ - Frontend test suite

## API Endpoints Added
- GET/POST /api/config - Server configuration
- GET/POST /api/claude/config - Claude CLI configuration
- POST /api/models/config - Model alias/hidden settings
- GET /api/accounts - Account list with status
- POST /api/accounts/:email/toggle - Enable/disable account
- POST /api/accounts/:email/refresh - Refresh account token
- DELETE /api/accounts/:email - Remove account
- GET /api/logs - Log history
- GET /api/logs/stream - Live log streaming (SSE)
- GET /api/auth/url - OAuth URL generation
- GET /oauth/callback - OAuth callback handler

## Backward Compatibility
- Default port remains 8080
- All existing CLI/API functionality unchanged
- WebUI is entirely optional
- Can be disabled by removing mountWebUI() call

tests/frontend/test-frontend-all.cjs

@@ -0,0 +1,85 @@
+/**
+ * Frontend Test Runner
+ * Runs all frontend test suites
+ * 
+ * Run: node tests/frontend/test-frontend-all.cjs
+ */
+
+const { execSync, spawn } = require('child_process');
+const path = require('path');
+
+const testFiles = [
+    'test-frontend-dashboard.cjs',
+    'test-frontend-logs.cjs',
+    'test-frontend-accounts.cjs',
+    'test-frontend-settings.cjs'
+];
+
+async function runTests() {
+    console.log('🚀 Running All Frontend Tests\n');
+    console.log('═'.repeat(60));
+
+    let totalPassed = 0;
+    let totalFailed = 0;
+    const results = [];
+
+    for (const testFile of testFiles) {
+        const testPath = path.join(__dirname, testFile);
+        console.log(`\n📋 Running: ${testFile}`);
+        console.log('─'.repeat(60));
+
+        try {
+            const output = execSync(`node "${testPath}"`, {
+                encoding: 'utf8',
+                stdio: ['pipe', 'pipe', 'pipe']
+            });
+            console.log(output);
+
+            // Parse results from output
+            const match = output.match(/Results: (\d+) passed, (\d+) failed/);
+            if (match) {
+                const passed = parseInt(match[1]);
+                const failed = parseInt(match[2]);
+                totalPassed += passed;
+                totalFailed += failed;
+                results.push({ file: testFile, passed, failed, status: 'completed' });
+            }
+        } catch (error) {
+            console.log(error.stdout || '');
+            console.log(error.stderr || '');
+
+            // Try to parse results even on failure
+            const output = error.stdout || '';
+            const match = output.match(/Results: (\d+) passed, (\d+) failed/);
+            if (match) {
+                const passed = parseInt(match[1]);
+                const failed = parseInt(match[2]);
+                totalPassed += passed;
+                totalFailed += failed;
+                results.push({ file: testFile, passed, failed, status: 'completed with errors' });
+            } else {
+                results.push({ file: testFile, passed: 0, failed: 1, status: 'crashed' });
+                totalFailed++;
+            }
+        }
+    }
+
+    console.log('\n' + '═'.repeat(60));
+    console.log('📊 SUMMARY\n');
+
+    for (const result of results) {
+        const icon = result.failed === 0 ? '✅' : '❌';
+        console.log(`${icon} ${result.file}: ${result.passed} passed, ${result.failed} failed (${result.status})`);
+    }
+
+    console.log('\n' + '─'.repeat(60));
+    console.log(`Total: ${totalPassed} passed, ${totalFailed} failed`);
+    console.log('═'.repeat(60));
+
+    process.exit(totalFailed > 0 ? 1 : 0);
+}
+
+runTests().catch(err => {
+    console.error('Test runner crashed:', err);
+    process.exit(1);
+});