Add clang-format-19 CI workflow with PR review suggestions

[Copilot]

Introduces a dedicated clang-format workflow that enforces formatting with clang-format-19 and surfaces suggested fixes directly on pull requests. The workflow mirrors the ulight pattern while adapting file selection to this repository’s tracked C/C++ sources.

• Workflow scope and triggers

  • Added .github/workflows/clang-format.yml
  • Runs on push and pull_request to main
  • Uses explicit permissions for checks/issues/PR annotations

• Formatting enforcement

  • Installs clang-format-19 on ubuntu-latest
  • Formats tracked *.c, *.cpp, *.h, *.hpp files via git ls-files
  • Fails when formatting drift exists using git diff --exit-code

• PR review suggestions

  • On pull requests, runs reviewdog/action-suggester@v1
  • Publishes inline suggested changes derived from formatting edits

- name: Run clang-format
  run: >
    git ls-files '*.cpp' '*.c' '*.hpp' '*.h' |
    xargs -r clang-format-19 -i

- name: Suggest clang-format fixes
  if: github.event_name == 'pull_request'
  uses: reviewdog/action-suggester@v1
  with:
    tool_name: clang-format-19
    fail_level: any
    level: warning