Add Chrome extension cookie bridge for session import

Users logged into Alta in Chrome can now send their session cookie
to the running Electron app via a local HTTP server on port 18247,
eliminating the need for re-authentication.

- main.js: HTTP cookie server with CORS, token, domain validation
- preload.js: onExtensionCookie push-pattern IPC bridge
- renderer.js: handleExtensionCookie sets session, fetches devices
- chrome-extension/: Manifest V3 extension with popup UI
- CLAUDE.md: updated architecture docs

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

preload.js

@@ -20,5 +20,16 @@ contextBridge.exposeInMainWorld('electronAPI', {
   stopCameraProxy: (processId) => ipcRenderer.invoke('camera-proxy-stop', { processId }),
   checkCameraProxy: () => ipcRenderer.invoke('camera-proxy-check'),
   getCameraProxyVersion: () => ipcRenderer.invoke('camera-proxy-version'),
-  listActiveCameraProxies: () => ipcRenderer.invoke('camera-proxy-list-active')
+  listActiveCameraProxies: () => ipcRenderer.invoke('camera-proxy-list-active'),
+
+  // Extension cookie bridge (push from main process)
+  onExtensionCookie: (callback) => {
+    ipcRenderer.on('extension-cookie-received', (event, data) => {
+      try {
+        callback(data);
+      } catch (error) {
+        console.error('Extension cookie handler error:', error);
+      }
+    });
+  }
 });