Add simple web UI for browsing the registry (#757)

## Summary

Adds a clean, minimal web interface at `/` for browsing MCP servers in
the registry. Built as a single self-contained HTML file embedded in the
Go binary.

## Features

- Responsive grid layout (1/2/3 columns based on screen size)
- Search servers by name
- Filter to show only latest versions (default on)
- "Recently Updated" section for servers updated in the last hour
- Expandable cards with full server metadata and JSON viewer
- Debug modal to switch between production/staging/local/custom API
endpoints
- Full URL parameter support and browser history navigation

## Implementation

- Single HTML file (~400 lines) with Tailwind CSS via CDN
- Zero build dependencies
- Embedded using `//go:embed` 
- Served directly from router at root path
- Uses stable v0.1 API endpoints

Fixes #99

---

AI disclosure: this is 99% vibed with Claude. It's intended as a v0 to
get something up and working, and then maybe at a later date we can
replace it with something more real.

internal/api/router/router.go

@@ -184,14 +184,19 @@ func NewHumaAPI(cfg *config.Config, registry service.RegistryService, mux *http.
 	// Add /metrics for Prometheus metrics using promhttp
 	mux.Handle("/metrics", metrics.PrometheusHandler())
 
-	// Add redirect from / to docs and 404 handler for all other routes
+	// Add UI and 404 handler for all other routes
 	mux.HandleFunc("/", func(w http.ResponseWriter, r *http.Request) {
 		if r.URL.Path == "/" {
-			http.Redirect(w, r, "https://github.com/modelcontextprotocol/registry/tree/main/docs", http.StatusTemporaryRedirect)
+			// Serve UI at root
+			w.Header().Set("Content-Type", "text/html; charset=utf-8")
+			_, err := w.Write([]byte(v0.GetUIHTML()))
+			if err != nil {
+				http.Error(w, "Failed to write response", http.StatusInternalServerError)
+			}
 			return
 		}
 
-		// Handle 404 for all other routes
+		// Handle 404 for all non-matched routes
 		handle404(w, r)
 	})