ci: add link checker, README convention check and PR templat

.github/workflows/link-check.yml

@@ -0,0 +1,44 @@
+name: Link check
+
+on:
+  schedule:
+    - cron: "0 6 * * 1"
+  pull_request:
+    paths:
+      - "**/*.md"
+      - ".github/lychee.toml"
+  workflow_dispatch:
+
+permissions:
+  contents: read
+  issues: write
+
+concurrency:
+  group: ${{ github.workflow }}-${{ github.ref }}
+  cancel-in-progress: true
+
+jobs:
+  lychee:
+    name: Check links
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+
+      - name: Check links
+        id: lychee
+        uses: lycheeverse/lychee-action@v2
+        with:
+          args: --config .github/lychee.toml --no-progress "**/*.md"
+          output: lychee/out.md
+          # Pull requests report broken links without blocking; scheduled runs fail and open an issue.
+          fail: ${{ github.event_name != 'pull_request' }}
+        env:
+          GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
+
+      - name: Report broken links
+        if: github.event_name != 'pull_request' && steps.lychee.outputs.exit_code != 0
+        uses: peter-evans/create-issue-from-file@v5
+        with:
+          title: Link check report
+          content-filepath: lychee/out.md
+          labels: broken-links