ci(packaging): automate AUR publish on Release (#507)

[Reei-dp]

Add aur-publish workflow, publish-aur job in Release, PKGBUILD sync in version-bump, and scripts/linux/aur_publish.sh for push + .SRCINFO generation.

Summary

Linked issue

Closes #

Checklist

• flutter analyze and flutter test pass locally
• Scope matches the linked issue only (no drive-by refactors)
• PR targets dev (not main, unless hotfix)

Metadata (automation)

If the branch is issue/<n>-… or the body contains Closes #n, workflow PR linked issue metadata copies labels and milestone from the linked issue onto this PR.

For Theme system work, ensure the issue has milestone Theme system and labels such as theme, editor, enhancement.

Manual override when creating the PR:

gh pr create --base dev \
  --milestone "Theme system" \
  --label "theme,enhancement" \
  --title "feat(theme): short description (#NN)" \
  --body "$(cat <<'EOF'
## Summary
...

Closes #NN
EOF
)"

[ZhuchkaTriplesix]

Great job, bro. <3