chore: delete root settings.yml and update CODEOWNERS

[jflowers]

Description

Remove the legacy root settings.yml (probot/settings format) which is superseded by the new safe-settings/ directory. Update CODEOWNERS to match the zero-dot-force standard.

Acceptance Criteria

• Root settings.yml deleted
• CODEOWNERS updated:
  • Add * catch-all line → @jflowers @marcusburghardt
  • Add safe-settings/ line → @jflowers @marcusburghardt
  • Keep org/ and .github/ lines
  • Remove settings.yml line (file no longer exists)

Context

The old settings.yml used the probot/settings format with repository:, labels:, and branches: blocks. This is replaced by:

• safe-settings/settings.yml — org-wide defaults
• safe-settings/deployment-settings.yml — deployment config
• safe-settings/suborgs/ — repo groupings
• safe-settings/repos/ — per-repo overrides