set up new workflow and migrate to .forgejo dir

.github/workflows/pr.yml

@@ -1,34 +0,0 @@
-name: PR Gate
-
-on:
-  pull_request:
-    branches:
-      - main
-
-concurrency:
-  group: ${{ github.workflow }}-${{ github.event.number || github.sha }}
-  cancel-in-progress: true
-
-permissions:
-  contents: read # to fetch code (actions/checkout)
-
-jobs:
-  checks:
-    name: Checks
-    runs-on: ubuntu-24.04
-    steps:
-      - name: Checkout
-        uses: actions/checkout@v4
-      - uses: pnpm/setup@v1
-        with:
-          version: 11
-          runtime: node@24
-          cache: true
-      - name: Lint
-        run: pnpm lint
-      - name: Svelte Check
-        run: pnpm check
-      - name: Test
-        run: pnpm run test:unit
-      - name: Build
-        run: pnpm run build