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/composites/code-opus-tdd-repo/v1/harness.yaml

@@ -0,0 +1,14 @@
+kind: composite
+name: code-opus-tdd-repo
+version: 1
+description: "Opus code agent with TDD enforcement — tests locked read-only, must pass before finish"
+
+layers:
+  - context: code-methodology/v1
+  - context: anthropic-cloud/v1
+  - context: gitea-ssh/v1
+  - context: agent-repo/v1
+  - context: tdd-protect/v1
+  - context: tdd-gate/v1
+  - capability: python-dev/v1
+  - capability: tdd-file-lock/v1