docs: add mailbox-first collaboration model

minions/chat/topic-thread-template.md

@@ -1,6 +1,8 @@
-## PM Request
+# PM Topic Summary Template
 
-TARGET ROLE:
+Related packets:
+
+- `minions/mail/YYYY-MM-DD-sender-to-recipient-topic/`
 
 DECISION:
 
@@ -8,38 +10,10 @@ RATIONALE:
 
 ACTION NEEDED:
 
-### AM
+NEXT OWNER:
 
-No action needed yet.
+## Summary
 
-### CM
-
-No action needed yet.
-
-### SM
-
-No action needed yet.
-
-### OM-Test / OM
-
-No action needed yet.
-
-### Operator
-
-No action needed until PM reviews the response.
-
----
-
-## Response
-
-Architecture findings / proposal / implementation report goes here.
-
----
-
-## PM Review
-
-DECISION:
-
-RATIONALE:
-
-ACTION NEEDED:
+- what changed:
+- key evidence:
+- remaining risk: