release: split the GitHub notes from the store changelog

The GitHub release body was the 500-char store changelog. Give the
GitHub release its own detailed notes under docs/releases/<tag>.md and
point release.yml at it, leaving the store changelog to be the trimmed
version plus a link back to the GitHub release.

The notes cover everything since 3.0.0, including ReplayGain, the artist
page work, the sort name preference and the fixes.

The store changelog still must exist; the workflow now checks both
files.

.github/workflows/release.yml

@@ -85,7 +85,9 @@ jobs:
             echo "value=false" >> "$GITHUB_OUTPUT"
           fi
       - name: Check release notes exist
-        run: test -f "metadata/en-US/changelogs/${{ needs.build.outputs.version-code }}.txt"
+        run: |
+          test -f "metadata/en-US/changelogs/${{ needs.build.outputs.version-code }}.txt"
+          test -f "docs/releases/$GITHUB_REF_NAME.md"
       - name: Write Play service account
         if: steps.stable.outputs.value == 'true'
         env:
@@ -123,7 +125,7 @@ jobs:
         env:
           GH_TOKEN: ${{ secrets.GITHUB_TOKEN }}
         run: |
-          args=(--verify-tag --title "$GITHUB_REF_NAME" --notes-file "metadata/en-US/changelogs/${{ needs.build.outputs.version-code }}.txt")
+          args=(--verify-tag --title "$GITHUB_REF_NAME" --notes-file "docs/releases/$GITHUB_REF_NAME.md")
           if [ "${{ steps.stable.outputs.value }}" != "true" ]; then
             args+=(--prerelease)
           fi