feat: Add branch-based beta toggle for switching between stable and beta versions

Adds Version Channel section to Settings sidebar allowing users to:
- See current branch (main or beta/7.0) and stability status
- Switch to beta branch to access Endless Mode features
- Switch back to stable for production use
- Pull updates for current branch

Implementation:
- BranchManager.ts: Git operations for branch detection/switching
- worker-service.ts: /api/branch/* endpoints (status, switch, update)
- Sidebar.tsx: Version Channel UI with branch state and handlers

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

src/services/worker-service.ts

@@ -29,6 +29,7 @@ import { SSEBroadcaster } from './worker/SSEBroadcaster.js';
 import { SDKAgent } from './worker/SDKAgent.js';
 import { PaginationHelper } from './worker/PaginationHelper.js';
 import { SettingsManager } from './worker/SettingsManager.js';
+import { getBranchInfo, switchBranch, pullUpdates, type BranchInfo, type SwitchResult } from './worker/BranchManager.js';
 
 export class WorkerService {
   private app: express.Application;
@@ -173,6 +174,11 @@ export class WorkerService {
     this.app.get('/api/mcp/status', this.handleGetMcpStatus.bind(this));
     this.app.post('/api/mcp/toggle', this.handleToggleMcp.bind(this));
 
+    // Branch switching (beta toggle)
+    this.app.get('/api/branch/status', this.handleGetBranchStatus.bind(this));
+    this.app.post('/api/branch/switch', this.handleSwitchBranch.bind(this));
+    this.app.post('/api/branch/update', this.handleUpdateBranch.bind(this));
+
     // Search API endpoints (for skill-based search)
     // Unified endpoints (new consolidated API)
     this.app.get('/api/search', this.handleUnifiedSearch.bind(this));
@@ -1035,6 +1041,89 @@ export class WorkerService {
     }
   }
 
+  // ============================================================================
+  // Branch Switching Handlers (Beta Toggle)
+  // ============================================================================
+
+  /**
+   * GET /api/branch/status - Get current branch information
+   */
+  private handleGetBranchStatus(req: Request, res: Response): void {
+    try {
+      const info = getBranchInfo();
+      res.json(info);
+    } catch (error) {
+      logger.failure('WORKER', 'Failed to get branch status', {}, error as Error);
+      res.status(500).json({ error: (error as Error).message });
+    }
+  }
+
+  /**
+   * POST /api/branch/switch - Switch to a different branch
+   * Body: { branch: "main" | "beta/7.0" }
+   */
+  private async handleSwitchBranch(req: Request, res: Response): Promise<void> {
+    try {
+      const { branch } = req.body;
+
+      if (!branch) {
+        res.status(400).json({ success: false, error: 'Missing branch parameter' });
+        return;
+      }
+
+      // Validate branch name
+      const allowedBranches = ['main', 'beta/7.0'];
+      if (!allowedBranches.includes(branch)) {
+        res.status(400).json({
+          success: false,
+          error: `Invalid branch. Allowed: ${allowedBranches.join(', ')}`
+        });
+        return;
+      }
+
+      logger.info('WORKER', 'Branch switch requested', { branch });
+
+      const result = await switchBranch(branch);
+
+      if (result.success) {
+        // Schedule worker restart after response is sent
+        setTimeout(() => {
+          logger.info('WORKER', 'Restarting worker after branch switch');
+          process.exit(0); // PM2 will restart the worker
+        }, 1000);
+      }
+
+      res.json(result);
+    } catch (error) {
+      logger.failure('WORKER', 'Branch switch failed', {}, error as Error);
+      res.status(500).json({ success: false, error: (error as Error).message });
+    }
+  }
+
+  /**
+   * POST /api/branch/update - Pull latest updates for current branch
+   */
+  private async handleUpdateBranch(req: Request, res: Response): Promise<void> {
+    try {
+      logger.info('WORKER', 'Branch update requested');
+
+      const result = await pullUpdates();
+
+      if (result.success) {
+        // Schedule worker restart after response is sent
+        setTimeout(() => {
+          logger.info('WORKER', 'Restarting worker after branch update');
+          process.exit(0); // PM2 will restart the worker
+        }, 1000);
+      }
+
+      res.json(result);
+    } catch (error) {
+      logger.failure('WORKER', 'Branch update failed', {}, error as Error);
+      res.status(500).json({ success: false, error: (error as Error).message });
+    }
+  }
+
   // ============================================================================
   // Search API Handlers (for skill-based search)
   // ============================================================================