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. -->

e2e-tests/snapshots/github-import.spec.ts_should-import-from-URL-1.aria.yml

@@ -0,0 +1,14 @@
+- paragraph: /Generate an AI_RULES\.md file for this app\. Describe the tech stack in 5-\d+ bullet points and describe clear rules about what libraries to use for what\./
+- img
+- text: file1.txt
+- button "Edit":
+  - img
+- img
+- text: file1.txt
+- paragraph: More EOM
+- button:
+  - img
+- img
+- text: less than a minute ago
+- button "Retry":
+  - img

e2e-tests/snapshots/github-import.spec.ts_should-import-from-repository-list-1.aria.yml

@@ -0,0 +1,14 @@
+- paragraph: /Generate an AI_RULES\.md file for this app\. Describe the tech stack in 5-\d+ bullet points and describe clear rules about what libraries to use for what\./
+- img
+- text: file1.txt
+- button "Edit":
+  - img
+- img
+- text: file1.txt
+- paragraph: More EOM
+- button:
+  - img
+- img
+- text: less than a minute ago
+- button "Retry":
+  - img