Fail startup when the HTTP listener cannot bind (closes #167)

The HTTP server ran ListenAndServe in a goroutine, so a failed bind
was only logged and neoircd kept running without its HTTP API.

The start hook now binds the listen address and returns the bind
error, so neoircd exits 1 with an error naming the address. If serving
the bound listener later ends with anything other than a normal
shutdown, the server stops the app through fx.Shutdowner with exit
code 1; the handler tests now pass it that Shutdowner.

Tests check that a taken port fails startup, that a serve failure
stops the app with exit code 1, and that a normal stop does not. The
server tests no longer run in parallel: building the app writes the
global viper instance.

Model: opus-5-5

internal/server/export_test.go

@@ -1,6 +1,10 @@
 package server
 
-import "github.com/go-chi/chi/v5"
+import (
+	"net"
+
+	"github.com/go-chi/chi/v5"
+)
 
 // NewTestSPAServer creates a Server whose router serves only
 // the embedded web client.
@@ -10,3 +14,9 @@ func NewTestSPAServer() *Server {
 
 	return srv
 }
+
+// ServeUntilShutdown runs serveUntilShutdown, which serves the
+// HTTP server on listener, and returns when it does.
+func (srv *Server) ServeUntilShutdown(listener net.Listener) {
+	srv.serveUntilShutdown(listener)
+}