chore: remove non-functional tunnel placeholder code

Removed incomplete tunnel implementation that was returning fake URLs.
- Removed tunnel:start and tunnel:stop IPC handlers from main process
- Removed tunnel API from preload contextBridge
- Added documentation comment noting tunnel feature is planned for Phase 6
- Tunnel UI settings remain in place for future implementation

The tunnel feature is documented as a planned Phase 6 feature in PRD.md
and CLAUDE.md:385. This change removes the non-functional placeholder
code from production while keeping the UI settings for future use.

Resolves housekeeping task #8

src/main/index.ts

@@ -197,21 +197,10 @@ function setupIpcHandlers() {
     }
   });
 
-  // Tunnel management (placeholder - will integrate ngrok/cloudflare)
-  ipcMain.handle('tunnel:start', async (_event, port: number, provider: string) => {
-    // TODO: Implement actual tunnel spawning
-    console.log(`Starting tunnel on port ${port} with ${provider}`);
-    return {
-      url: `https://mock-${Math.random().toString(36).substr(2, 9)}.ngrok.io`,
-      active: true,
-    };
-  });
-
-  ipcMain.handle('tunnel:stop', async (_event, sessionId: string) => {
-    // TODO: Implement tunnel cleanup
-    console.log(`Stopping tunnel for session ${sessionId}`);
-    return true;
-  });
+  // Tunnel management
+  // NOTE: Tunnel feature is planned for Phase 6 (see PRD.md and CLAUDE.md:385)
+  // When implemented, will support ngrok/cloudflare for remote access
+  // Remove this comment when implementing the feature
 
   // Web server management
   ipcMain.handle('webserver:getUrl', async () => {

src/main/preload.ts

@@ -40,12 +40,6 @@ contextBridge.exposeInMainWorld('maestro', {
     readFile: (filePath: string) => ipcRenderer.invoke('fs:readFile', filePath),
   },
 
-  // Tunnel API
-  tunnel: {
-    start: (port: number, provider: string) => ipcRenderer.invoke('tunnel:start', port, provider),
-    stop: (sessionId: string) => ipcRenderer.invoke('tunnel:stop', sessionId),
-  },
-
   // Web Server API
   webserver: {
     getUrl: () => ipcRenderer.invoke('webserver:getUrl'),
@@ -104,10 +98,6 @@ export interface MaestroAPI {
     readDir: (dirPath: string) => Promise<any[]>;
     readFile: (filePath: string) => Promise<string>;
   };
-  tunnel: {
-    start: (port: number, provider: string) => Promise<{ url: string; active: boolean }>;
-    stop: (sessionId: string) => Promise<boolean>;
-  };
   webserver: {
     getUrl: () => Promise<string>;
   };