Add tdd-gate context, *-code-tdd-repo composites, and TDD task templates

Adds the tdd-gate harness context (TEST_PASS_REQUIRED=true + CLAUDE.md
methodology) and five provider-specific TDD composites that layer
tdd-protect + tdd-gate + python-dev + tdd-file-lock on top of the
existing code-* layer stacks. Matching task templates for sonnet, opus,
haiku, minimax, and airouter. allowed_failing_tests support noted in
warnings pending M19 pre-test hook implementation.

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

harnesses/contexts/tdd-gate/v1/harness.yaml

@@ -0,0 +1,13 @@
+kind: context
+name: tdd-gate
+version: 1
+description: "TDD enforcement: agent must get all tests passing before finishing. Compose on top of code-methodology."
+requires: []
+provides: [tdd-gate]
+
+env:
+  TEST_PASS_REQUIRED: "true"
+
+context_files:
+  - source: ./CLAUDE.md
+    target: /opt/harness/context/tdd-gate/CLAUDE.md