feat(tarpit): port-selective tc netem tarpit mode with live log events

- GET/POST/DELETE /api/v1/deckies/{name}/tarpit (admin write, viewer GET)
- get_container_veth() + get_container_pid() in network.py via iflink/ip-link
- TarpitRule SQLModel table + TarpitMixin repo (upsert/get/delete/list)
- Background tarpit_watcher_worker: polls /proc/{pid}/net/tcp every 15s,
  emits tarpit_enter/tarpit_exit log events (edge-triggered, with duration)
- tarpit_enabled/tarpit_disabled logs on operator POST/DELETE actions

decnet/web/db/sqlmodel_repo/__init__.py

@@ -48,6 +48,7 @@ from decnet.web.db.sqlmodel_repo.orchestrator import OrchestratorMixin
 from decnet.web.db.sqlmodel_repo.realism import RealismMixin
 from decnet.web.db.sqlmodel_repo.swarm import SwarmMixin
 from decnet.web.db.sqlmodel_repo.topology import TopologyMixin
+from decnet.web.db.sqlmodel_repo.tarpit import TarpitMixin
 from decnet.web.db.sqlmodel_repo.webhooks import WebhooksMixin
 
 
@@ -66,6 +67,7 @@ class SQLModelRepository(
     OrchestratorMixin,
     RealismMixin,
     SwarmMixin,
+    TarpitMixin,
     TopologyMixin,
     WebhooksMixin,
     BaseRepository,