fix: migrate to tailwind v4 and TS6, add oauth2 dashboard_host setting

- migrate Tailwind v3->v4 (postcss @tailwindcss/postcss, CSS-first @theme/@plugin/@custom-variant)
- fix TS6 build: ignoreDeprecations for baseUrl, react-day-picker v10 classNames, test type fixes
- add dashboard_host setting field with i18n

postcss.config.js

@@ -1,6 +1,5 @@
 export default {
     plugins: {
-        tailwindcss: {},
-        autoprefixer: {},
+        "@tailwindcss/postcss": {},
     },
 }