Phase 3 part 1: Add interactive API explorer
- Create templates/api_explorer.templ with mock and real modes
- Add EndpointInfo and APIExplorerData types to templates/types.go
- Fix markdown rendering with UnsafeHTML.ToComponent()
- Add templ import for Component support
- API explorer supports:
- Mock data mode for non-authenticated users
- Real execution mode for logged-in users
- Request/response display
- cURL generation
- Copy to clipboard
