Add agentic workflows for community catalog submissions (#2655)

* Add agentic workflows for community catalog submissions

Add GitHub Agentic Workflows that automatically process community
extension and preset submission issues:

- add-community-extension.md: triggered by extension-submission issues,
  validates the submission, updates extensions/catalog.community.json
  and docs/community/extensions.md, then opens a draft PR
- add-community-preset.md: parallel workflow for preset-submission
  issues, updates presets/catalog.community.json and
  docs/community/presets.md

Both workflows:
- Trigger on opened, edited, or labeled events (maintainers can
  retroactively label pre-existing issues)
- Validate ID format, semver, repo existence, required files, release,
  and submission checklists
- Label issues with validation-passed or validation-failed
- Create draft PRs with Closes #N for maintainer review

Also includes gh-aw scaffolding (.github/aw/, .gitattributes lock file
rule, dependabot ignore for gh-aw-actions).

* Suppress whitespace checks on generated .lock.yml files

These files are auto-generated by gh aw compile and contain trailing
whitespace in the ASCII art header and indented YAML blocks that we
cannot control. Add -whitespace attribute to skip git whitespace
checks on them.