build: update to node 22 and pnpm (#3616)

This commit brings the project to support node 22 which became LTS and
fixes broken builds with typescript 5.7+ until vue-tsc is updated and
replaces npm with pnpm.

- Update tsconfig for node 22
- Pin typescript to 5.6.x to not break vue-tsc
- Replace npm with pnpm (corepack recommended)
- Update Makefile and main workflow for pnpm
- Migrate to eslint 9 flat config
- Fix broken imports
- Exclude non-TS vue files for vue-tsc

frontend/src/components/settings/Themes.vue

@@ -7,7 +7,7 @@
 </template>
 
 <script setup lang="ts">
-import { SelectHTMLAttributes } from "vue";
+import type { SelectHTMLAttributes } from "vue";
 import { useI18n } from "vue-i18n";
 
 const { t } = useI18n();