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/hot-memory.md

@@ -1,5 +1,5 @@
-# Hot Memory
 <!-- L0: Cross-domain strategic context — identity, active priorities -->
+# Hot Memory
 
 <!-- Rewrite freely. Keep under 50 lines. -->
 <!-- Run /setup to populate this with your domains and priorities. -->