chore(ddev): add build-gitea-frontend command

`make backend` embeds public/ via go:embed at compile time, so any frontend
asset change requires:
  ddev build-gitea-frontend  # vite into public/assets/
  ddev build-gitea           # re-embed public/ into the binary
  ddev restart               # pick up new binary

.ddev/.gitignore

@@ -11,6 +11,7 @@ commands/*
 !commands/web/
 commands/web/*
 !commands/web/build-gitea
+!commands/web/build-gitea-frontend
 !gitea/
 gitea/*
 !gitea/app.ini

.ddev/commands/web/build-gitea-frontend

@@ -0,0 +1,11 @@
+#!/usr/bin/env bash
+## Description: Build the gitea frontend assets (CSS/JS) inside the web container
+## Usage: build-gitea-frontend
+## Example: ddev build-gitea-frontend
+
+set -eu
+cd /var/www/html
+echo "Installing frontend deps and building assets..."
+make deps-frontend
+make frontend
+echo "Done."