feat(tdd): inject session history into green and refactor worker prompts

Adds SessionsDir to tdd.Config, session_id to tool input schemas, and a
prependHistory method that reads the session JSONL log and prepends a
formatted history block to the task prompt before worker invocation.

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

cmd/supervisor/main.go

@@ -67,6 +67,7 @@ func main() {
 		SkillPrompt:  string(tddPrompt),
 		DefaultModel: models.Resolve("tdd", ""),
 		ExecutorFn:   executor.Run,
+		SessionsDir:  cfg.SessionsDir,
 	}))
 	reg.Register(brain.New(brain.Config{
 		IngestBaseURL: cfg.IngestBaseURL,