Add MiniMax test-writing composite and template

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

harnesses/composites/test-writing-minimax-repo/v1/harness.yaml

@@ -0,0 +1,11 @@
+kind: composite
+name: test-writing-minimax-repo
+version: 1
+description: "Test writing agent with MiniMax + repo clone via SSH"
+
+layers:
+  - context: test-writing/v1
+  - context: minimax-code-methodology/v1
+  - context: minimax/v1
+  - context: gitea-ssh/v1
+  - context: agent-repo/v1