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>

docs/technical/architecture/platform-topology.md

@@ -97,10 +97,10 @@ SUPPORTING
                               ▼
 ┌─────────────────────────────────────────────────────────────────────┐
 │                   ORCHESTRATION & WORKFLOW                           │
-│  ┌──────────────┐  ┌──────────────┐  ┌──────────────┐              │
-│  │ Scheduler    │  │ Orchestrator │  │ TaskRunner   │              │
-│  │(Job Sched)   │  │(Coordinator) │  │(Executor)    │              │
-│  └──────────────┘  └──────────────┘  └──────────────┘              │
+│  ┌──────────────┐  ┌──────────────┐                                │
+│  │ Scheduler    │  │ Orchestrator │                                │
+│  │(Job Sched)   │  │(Coordinator) │                                │
+│  └──────────────┘  └──────────────┘                                │
 └─────────────────────────────────────────────────────────────────────┘
                               │
                               ▼