docs(07-08): complete the avatar bucket publish plan

Serve and Handler now publish the uploads bucket; assembled avatar
POST is 200. Record the gap-closure outcome.

Co-authored-by: Cursor <cursoragent@cursor.com>

.planning/phases/07-user-plugin-and-authentication/07-08-PLAN.md

@@ -12,6 +12,7 @@ files_modified:
   - ../fonoteka.go/parity/genre_security_test.go
   - ../fonoteka.go/plugins/golem15/user/avatar_test.go
 autonomous: true
+gap_closure: true
 requirements: []
 user_setup: []