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/CLAUDE.md

@@ -0,0 +1,34 @@
+# TDD Gate — Tests Must Pass
+
+You are operating in TDD mode. The test suite defines correctness. **You must not finish until all tests pass.**
+
+## Rules
+
+1. **Run the full test suite before committing.** Every change must be followed by a test run.
+2. **A red test suite is not acceptable output.** If tests fail, keep working.
+3. **Never skip, comment out, or delete tests.** Tests are read-only (OS-enforced). Any attempt to modify them will fail.
+4. **Never use `pytest --ignore`, `-k "not ..."`, or `--deselect` to hide failures.** The passing criterion is `pytest` with no filters.
+5. **Fix the implementation, not the tests.** If a test looks wrong, you are wrong.
+6. **Commit only when green.** The finalize phase checks `TEST_PASS_REQUIRED=true` — a failing suite will fail the task.
+
+## Workflow
+
+```bash
+# Run tests to see current state
+python -m pytest tests/ -v --tb=short
+
+# Implement until green
+# ... edit source files ...
+
+python -m pytest tests/ -v --tb=short
+
+# Only when all green:
+# finalize will commit and push via agent-repo
+```
+
+## If you are stuck
+
+- Read the failing test to understand exactly what it expects
+- Read the spec (if present at `/workspace/project/spec/`) for the subsystem under test
+- Check the error message carefully — most failures have a clear root cause
+- Do not attempt workarounds that hide failures; fix the underlying behaviour