feat(subagent-dev): add TDD RED evidence to implementer report format

Add a conditional TDD Evidence field to the implementer report format so controllers can verify RED and GREEN output when TDD was required.

The field asks for the command run, relevant RED/GREEN output, and the expected RED failure reason rather than raw full logs.

Fixes #994.

skills/subagent-driven-development/implementer-prompt.md

@@ -103,6 +103,9 @@ Subagent (general-purpose):
     - **Status:** DONE | DONE_WITH_CONCERNS | BLOCKED | NEEDS_CONTEXT
     - What you implemented (or what you attempted, if blocked)
     - What you tested and test results
+    - **TDD Evidence** (if TDD was required for this task):
+      - RED: command run, relevant failing output before implementation, and why the failure was expected
+      - GREEN: command run and relevant passing output after implementation
     - Files changed
     - Self-review findings (if any)
     - Any issues or concerns