Initial vibeproxy implementation

Self-contained HTTP/HTTPS/TCP/UDP reverse proxy manager written in Go,
with SQLite storage, a Bootstrap 5 admin UI (Go templates, no JS
framework), and a REST API under /api/v1.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01QTXFrNP1imCW7jtfL5SZrw

internal/app/admin_server.go

@@ -0,0 +1,66 @@
+package app
+
+import (
+	"context"
+	"database/sql"
+	"errors"
+	"fmt"
+	"net/http"
+	"time"
+
+	"github.com/owen/vibeproxy/internal/metrics"
+)
+
+type adminServer struct {
+	srv *http.Server
+}
+
+func newAdminServer(addr string, handler http.Handler) *adminServer {
+	return &adminServer{srv: &http.Server{
+		Addr:         addr,
+		Handler:      handler,
+		ReadTimeout:  30 * time.Second,
+		WriteTimeout: 60 * time.Second,
+		IdleTimeout:  120 * time.Second,
+	}}
+}
+
+func (a *adminServer) Start(ctx context.Context) error {
+	errCh := make(chan error, 1)
+	go func() {
+		if err := a.srv.ListenAndServe(); err != nil && !errors.Is(err, http.ErrServerClosed) {
+			errCh <- fmt.Errorf("admin listener: %w", err)
+		}
+	}()
+	select {
+	case <-ctx.Done():
+		shutdownCtx, cancel := context.WithTimeout(context.Background(), 15*time.Second)
+		defer cancel()
+		return a.srv.Shutdown(shutdownCtx)
+	case err := <-errCh:
+		return err
+	}
+}
+
+func healthzHandler() http.Handler {
+	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		w.WriteHeader(http.StatusOK)
+		w.Write([]byte("ok"))
+	})
+}
+
+func readyzHandler(db *sql.DB) http.Handler {
+	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		if err := db.PingContext(r.Context()); err != nil {
+			w.WriteHeader(http.StatusServiceUnavailable)
+			w.Write([]byte("database unavailable"))
+			return
+		}
+		w.WriteHeader(http.StatusOK)
+		w.Write([]byte("ready"))
+	})
+}
+
+func metricsHandler() http.Handler {
+	return metrics.Handler()
+}