Notify question authors via Resend when an admin posts the first answer.

Require email at registration (editable on profile), add a Resend mailer with idempotent first-answer sends, and keep answer saves independent of delivery.

cmd/server/main.go

@@ -17,6 +17,7 @@ import (
 
 	"plumber"
 	"plumber/internal/blob"
+	"plumber/internal/mail"
 	"plumber/internal/store"
 	"plumber/internal/web"
 )
@@ -29,7 +30,11 @@ func main() {
 	defer sessions.Close()
 
 	uploader := blob.FromEnv()
-	handler := newHandler(db, sessions, uploader)
+	notifier, err := mail.FromEnv()
+	if err != nil {
+		log.Fatalf("mail: %v", err)
+	}
+	handler := newHandler(db, sessions, uploader, notifier)
 	run(&http.Server{
 		Addr:              listenAddr(),
 		Handler:           handler,
@@ -53,12 +58,13 @@ func openDB() (*sql.DB, *store.SessionStore) {
 	return db, sessions
 }
 
-func newHandler(db *sql.DB, sessions *store.SessionStore, uploader blob.Uploader) http.Handler {
+func newHandler(db *sql.DB, sessions *store.SessionStore, uploader blob.Uploader, notifier mail.Notifier) http.Handler {
 	srv, err := web.New(store.NewPostgres(db), sessions.Store(), plumber.TemplateFS, plumber.StaticFS, web.Config{
 		AdminSetupSecret: strings.TrimSpace(os.Getenv("ADMIN_SETUP_SECRET")),
 		SecureCookie:     secureCookieFromEnv(),
 		TrustedProxies:   parseTrustedProxies(os.Getenv("TRUSTED_PROXY_CIDRS")),
 		Blob:             uploader,
+		Mail:             notifier,
 	})
 	if err != nil {
 		log.Fatalf("server: %v", err)