fix(write-tests): reviewer_harness default → planning-minimax-repo/v1

planning/v1 is a bare context with no provider credentials; any review node
using it fails with "Not logged in". The correct composite is
planning-minimax-repo/v1 which includes minimax/v1 auth.

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

workflows/write-tests.yaml

@@ -42,8 +42,8 @@ params:
       description: "Harness for the test-writing node (default: test-writing-opus-repo/v1)"
     reviewer_harness:
       type: string
-      default: "planning/v1"
-      description: "Harness for the coverage review node (default: planning/v1)"
+      default: "planning-minimax-repo/v1"
+      description: "Harness for the coverage review node (default: planning-minimax-repo/v1)"
 
 nodes:
   write_tests: