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/observations.md

@@ -1,4 +1,4 @@
-# Personal — Observations
 <!-- L0: Timestamped observations and events -->
+# Personal — Observations
 
 <!-- Append-only. Format: - YYYY-MM-DD [tags]: observation -->