chore(memory): L0 line-1 convention — all files start with L0 summary

Migrated all memory files to have L0 comment as first line,
consistent with upstream PAI convention.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

memory/personal/entities.md

@@ -1,4 +1,4 @@
-# Personal — Entities
 <!-- L0: People, places, and things -->
+# Personal — Entities
 
 <!-- Edit in place by ### Name header. -->