Release v1.8.2

fix: Fix MSIX code-signing certificate issue for v1.8.2

• Replace certificate store reference with self-signed certificate generation
• Add PowerShell script to create self-signed certificate during GitHub Actions workflow
• Export certificate to .pfx file with temporary password for MSIX signing
• Update certificate_path to point to generated certificate file (demo_flutter_cert.pfx)
• Change store: true to store: false for development MSIX packages
• Remove --store flag from dart run msix:create command
• Enable MSIX packaging without requiring pre-installed certificates
• Resolve 'certificate not found in: STORE' error in GitHub Actions workflow
• Support development/testing MSIX packages without Microsoft Store requirements