Bring in mcp-skills-plugins branch: marketplace, plugins, skills, OpenCredits, and image previews

Major release adding:
- MCP marketplace with curated registry and search across multiple registries
- Plugins and skills marketplace integration
- OpenCredits payment integration with model selection and checkout flow
- Image preview before sending (paste, file picker)
- Self-hosted Umami analytics with custom events
- Support feedback modal with Discord webhook
- Local OpenAI to Anthropic router for model routing
- Inline stop button replacing send during processing
- Improved install flow requiring Node.js 18+
- WSL env var passthrough fixes
- Better error handling and Windows compatibility

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

.gitignore

@@ -3,4 +3,5 @@ dist
 node_modules
 .vscode-test/
 *.vsix
-backup
+backup
+backup-files