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>

frontend/src/api/networks.ts

@@ -0,0 +1,36 @@
+import api from "./client";
+
+export interface NetworkInfo {
+  id: string;
+  name: string;
+  driver: string;
+  scope: string;
+  internal: boolean;
+  attachable: boolean;
+  subnet: string | null;
+  gateway: string | null;
+  containers: string[];
+  in_use: boolean;
+  stack: string | null;
+  labels: Record<string, string>;
+  created: string | null;
+  is_default: boolean;
+}
+
+export interface NetworkCreate {
+  name: string;
+  driver: string;
+  subnet?: string | null;
+  gateway?: string | null;
+  internal: boolean;
+  attachable: boolean;
+}
+
+export const networksApi = {
+  list: () => api.get<NetworkInfo[]>("/api/networks").then((r) => r.data),
+  create: (body: NetworkCreate) =>
+    api.post<NetworkInfo>("/api/networks", body).then((r) => r.data),
+  remove: (id: string) => api.delete(`/api/networks/${id}`).then((r) => r.data),
+  prune: () =>
+    api.post<{ NetworksDeleted: string[] | null }>("/api/networks/prune").then((r) => r.data),
+};