feat(airouter): DeepSeek V4 Flash TDD composite + max-effort template

New code-airouter-deepseekv4flash-tdd-repo/v1 composite (deepseek
methodology + the same tdd-protect/tdd-gate/python-dev/tdd-file-lock
layers as the Qwen TDD composite), plus a task-template that sets
reasoning_effort=max via the new extra_body passthrough (agent-runtimes
TT-38). Model/endpoint/model-registry entries already existed; only
the TDD-capable harness and the template were missing.

harnesses/composites/code-airouter-deepseekv4flash-tdd-repo/v1/harness.yaml

@@ -0,0 +1,19 @@
+kind: composite
+name: code-airouter-deepseekv4flash-tdd-repo
+version: 1
+description: "Airouter DeepSeek V4 Flash code agent with TDD enforcement — tests locked read-only, must pass before finish"
+
+# Inherits airouter context's label gate — only the airouter dispatcher
+# advertises this composite (see dispatcher/poller._collect_supported_harnesses).
+requires_labels: [airouter]
+
+layers:
+  - context: deepseek-code-methodology/v1
+  - context: best-practices/v1
+  - context: airouter/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