feat(config): expand role_registry + fix T4 default runtime

Role registry additions:
- T2: add ai, security, mobile domains
- T3: add data, ai, security, mobile, database, devops, docs domains
- T4: add data (data-engineer), embedded (firmware-engineer)
- T5: add accessibility, e2e, frontend, data verifier roles

TeamRunner consistency fix:
- T4 briefs now default to 'coding_agent' runtime (Claude Code)
  per build spec: 'Claude Code as default T4 runtime'
  T3 can still override preferred_runtime per task

config/role_registry.yaml

@@ -6,12 +6,22 @@ t2:
   frontend: agents/engineering/engineering-software-architect.md
   infra:    agents/engineering/engineering-devops-automator.md
   data:     agents/engineering/engineering-data-engineer.md
+  ai:       agents/engineering/engineering-software-architect.md
+  security: agents/engineering/engineering-security-engineer.md
+  mobile:   agents/engineering/engineering-software-architect.md
   default:  agents/engineering/engineering-software-architect.md
 
 t3:
   backend:  agents/engineering/engineering-senior-developer.md
   frontend: agents/engineering/engineering-senior-developer.md
   infra:    agents/engineering/engineering-sre.md
+  data:     agents/engineering/engineering-data-engineer.md
+  ai:       agents/engineering/engineering-ai-engineer.md
+  security: agents/engineering/engineering-security-engineer.md
+  mobile:   agents/engineering/engineering-mobile-app-builder.md
+  database: agents/engineering/engineering-database-optimizer.md
+  devops:   agents/engineering/engineering-sre.md
+  docs:     agents/engineering/engineering-technical-writer.md
   default:  agents/engineering/engineering-senior-developer.md
 
 t4:
@@ -23,6 +33,8 @@ t4:
   ai:        agents/engineering/engineering-ai-engineer.md
   security:  agents/engineering/engineering-security-engineer.md
   docs:      agents/engineering/engineering-technical-writer.md
+  data:      agents/engineering/engineering-data-engineer.md
+  embedded:  agents/engineering/engineering-embedded-firmware-engineer.md
   default:   agents/engineering/engineering-senior-developer.md
 
 t5:
@@ -31,4 +43,8 @@ t5:
   api:           agents/testing/testing-api-tester.md
   performance:   agents/testing/testing-performance-benchmarker.md
   security:      agents/engineering/engineering-security-engineer.md
+  accessibility: agents/testing/testing-accessibility-auditor.md
+  e2e:           agents/testing/testing-evidence-collector.md
+  frontend:      agents/testing/testing-accessibility-auditor.md
+  data:          agents/testing/testing-reality-checker.md
   default:       agents/engineering/engineering-code-reviewer.md

core/team_runner.py

@@ -554,7 +554,9 @@ class TeamRunner:
         briefs: list[TaskBrief] = []
         for task in tasks:
             role = task.get("role", "default")
-            pref_runtime = task.get("preferred_runtime", "standard")
+            # T4 is the coding/implementation tier; default to coding_agent
+            # so implementers use Claude Code unless T3 explicitly overrides.
+            pref_runtime = task.get("preferred_runtime", "coding_agent")
             brief = parent.make_child_brief(
                 tier=4,
                 role=role,