GitHub Import Feature: Import repositories/projects from GitHub (#1424) (#1454)

## Summary
Adds the ability to import GitHub repositories directly into Dyad from
the home screen, complementing the existing local folder import feature.
- GitHub Import Modal: New modal accessible from home screen via "Import
from Github" button with two Import methods
- Select project from GitHub repositories list
- Clone from any GitHub URL
- Advanced Options: Optional custom install/start commands (defaults to
project's package.json scripts)
- Auto AI_RULES Generation: Automatically generates AI_RULES.md if not
present in imported repo

closes #1424
    
<!-- This is an auto-generated description by cubic. -->
---

## Summary by cubic
Adds a GitHub import flow from the home screen so users can clone repos
via their list or any URL, with optional install/start commands and
automatic AI_RULES.md generation. Addresses Linear #1424 by enabling
seamless project setup from GitHub.

- **New Features**
  - Import modal with two tabs: Your Repositories and From URL.
- Advanced options for install/start commands with validation; defaults
used when both are empty.
- After cloning, navigate to chat and auto-generate AI_RULES.md if
missing.
- New IPC handler github:clone-repo-from-url with token auth support,
plus IpcClient method and preload channel.
- E2E tests cover modal open, auth, import via URL/repo list, and
advanced options.

- **Dependencies**
  - Added @radix-ui/react-tabs for the modal tab UI.

<!-- End of auto-generated description by cubic. -->

package.json

@@ -115,6 +115,7 @@
     "@radix-ui/react-separator": "^1.1.2",
     "@radix-ui/react-slot": "^1.2.2",
     "@radix-ui/react-switch": "^1.2.0",
+    "@radix-ui/react-tabs": "^1.0.4",
     "@radix-ui/react-toggle": "^1.1.3",
     "@radix-ui/react-toggle-group": "^1.1.3",
     "@radix-ui/react-tooltip": "^1.1.8",