feat(cli): prioritize GitHub release download with fallback to bundled assets (#81)

- Add GitHubRateLimitError and GitHubDownloadError for better error handling
- Detect rate limits (403 with remaining=0, 429)
- Try downloading from GitHub releases first
- Fall back to bundled assets on network error, rate limit, or download failure
- Add --offline flag to skip GitHub download
- Use GitHub auto-generated archive URL as fallback when no ZIP asset exists
- Update CLI to v1.9.0

Co-authored-by: Claude Opus 4.5 <noreply@anthropic.com>

README.md

@@ -49,7 +49,7 @@ uipro init --ai all         # All assistants
 ```bash
 uipro versions              # List available versions
 uipro update                # Update to latest version
-uipro init --version v1.0.0 # Install specific version
+uipro init --offline        # Skip GitHub download, use bundled assets
 ```
 
 ### Manual Installation