refactor(jobengine): delete TaskRunner service

- Remove TaskRunner source, tests, libraries (3 directories)
- Remove from compose, services-matrix, nginx, hosts, smoke tests
- Remove CLI commands, UI references, Authority scopes
- Remove docs, OpenAPI spec, QA state files
- Leave task_runner_id DB columns as nullable legacy
- PacksRegistry preserved (independent service)
- Eliminates 2 containers (taskrunner-web + taskrunner-worker)

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

devops/docker/services-matrix.env

@@ -40,9 +40,7 @@ riskengine-web|devops/docker/Dockerfile.hardened.template|src/Findings/StellaOps
 riskengine-worker|devops/docker/Dockerfile.hardened.template|src/Findings/StellaOps.RiskEngine.Worker/StellaOps.RiskEngine.Worker.csproj|StellaOps.RiskEngine.Worker|8080
 # ── Slot 17: Orchestrator (DECOMPOSED — see release-orchestrator + workflow) ──
 # orchestrator and orchestrator-worker removed; replaced by release-orchestrator (Slot 47) + workflow (Slot 46)
-# ── Slot 18: TaskRunner ─────────────────────────────────────────────────────────
-taskrunner-web|devops/docker/Dockerfile.hardened.template|src/JobEngine/StellaOps.TaskRunner/StellaOps.TaskRunner.WebService/StellaOps.TaskRunner.WebService.csproj|StellaOps.TaskRunner.WebService|8080
-taskrunner-worker|devops/docker/Dockerfile.hardened.template|src/JobEngine/StellaOps.TaskRunner/StellaOps.TaskRunner.Worker/StellaOps.TaskRunner.Worker.csproj|StellaOps.TaskRunner.Worker|8080
+# ── Slot 18: TaskRunner (REMOVED) ───────────────────────────────────────────────
 # ── Slot 19: Scheduler ──────────────────────────────────────────────────────────
 scheduler-web|devops/docker/Dockerfile.hardened.template|src/JobEngine/StellaOps.Scheduler.WebService/StellaOps.Scheduler.WebService.csproj|StellaOps.Scheduler.WebService|8080
 scheduler-worker|devops/docker/Dockerfile.hardened.template|src/JobEngine/StellaOps.Scheduler.Worker.Host/StellaOps.Scheduler.Worker.Host.csproj|StellaOps.Scheduler.Worker.Host|8080