Phase 9: network management + stack delete in UI (0.9.0)

- Networks: network_service (list w/ subnet/containers/in-use/owning-stack,
  create bridge/macvlan/ipvlan/overlay + optional subnet/gateway/internal,
  delete with default-network guard, prune) + routers/networks.py; real
  Networks page replaces the placeholder.
- Fix: local stacks can now be deleted from the UI — Delete button on stack
  detail (with optional keep-files-on-disk) and a trash action on stack cards,
  via a shared ConfirmDialog. (Backend DELETE existed; no UI surfaced it.)

Verified: py_compile, frontend tsc build, live network list smoke test
(defaults flagged, compose nets + in-use detected); main 104 routes.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

backend/main.py

@@ -21,6 +21,7 @@ from routers import (
     destinations,
     editor,
     images,
+    networks,
     ports,
     schedules,
     settings as settings_router,
@@ -53,7 +54,7 @@ async def lifespan(app: FastAPI):
     schedule_task.cancel()
 
 
-app = FastAPI(title="StackPilot", version="0.8.0", lifespan=lifespan)
+app = FastAPI(title="StackPilot", version="0.9.0", lifespan=lifespan)
 
 app.add_middleware(
     CORSMiddleware,
@@ -85,6 +86,7 @@ app.include_router(settings_router.router)
 app.include_router(backups.router)
 app.include_router(destinations.router)
 app.include_router(schedules.router)
+app.include_router(networks.router)
 app.include_router(agents.router)
 app.include_router(ws.router)