Build the HTTP router before the server starts (closes #104)

The fx OnStart hook started a goroutine that built the router and then
began serving, so OnStart returned before the router existed. Code that
served requests through the started Server, as the internal/handlers
tests do, raced with that goroutine or hit a nil router.

OnStart now configures the server, enables Sentry and builds the router
itself, and only then starts serving in the background. Sentry is set up
first because the routes depend on whether it is enabled. Run, whose
only caller was that hook, is folded into it.

Model: opus-5-5

internal/server/server.go

@@ -71,7 +71,14 @@ func New(
 	lifecycle.Append(fx.Hook{
 		OnStart: func(_ context.Context) error {
 			srv.startupTime = time.Now()
-			go srv.Run() //nolint:contextcheck
+
+			// Build the router before OnStart returns, so srv can
+			// handle requests as soon as the app has started.
+			srv.configure()
+			srv.enableSentry()
+			srv.SetupRoutes()
+
+			go srv.serve() //nolint:contextcheck
 
 			return nil
 		},
@@ -83,13 +90,6 @@ func New(
 	return srv, nil
 }
 
-// Run starts the server configuration, Sentry, and begins serving.
-func (srv *Server) Run() {
-	srv.configure()
-	srv.enableSentry()
-	srv.serve()
-}
-
 // ServeHTTP delegates to the chi router.
 func (srv *Server) ServeHTTP(
 	writer http.ResponseWriter,
@@ -202,8 +202,6 @@ func (srv *Server) serveUntilShutdown() {
 		Handler:        srv,
 	}
 
-	srv.SetupRoutes()
-
 	srv.log.Info(
 		"http begin listen", "listenaddr", listenAddr,
 	)