chore(github): add CODEOWNERS

Lands the CODEOWNERS file required by Plan §5.10. Single-developer
phase: every path falls back to the maintainer for review. Path-specific
overrides arrive once there is more than one human reviewer.

The matching branch-protection flip (require_code_owner_reviews: true)
is applied as a separate gh api call after this PR merges.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: UnbreakableMJ

.github/CODEOWNERS

@@ -0,0 +1,6 @@
+# Pearlite CODEOWNERS — required reviewers per Plan §5.10.
+# Format: <pattern> <space-separated owners>
+# Patterns follow .gitignore syntax; later matches win.
+
+# Default: every change requires the maintainer's review.
+* @UnbreakableMJ