Phase 11: remote UX & network attach (0.11.0)

- Live remote-stack logs over a WebSocket proxied through the central app to
  the agent (/ws/agent-logs/{agent}/{stack}); agent gains a WS log endpoint.
- Deploy to a remote host from the UI: host selector in the New Stack editor
  and template dialog; templates instantiate onto an agent via the proxy.
- Network attach/detach: expandable inspect view per network with
  connect/disconnect + container picker; GET /{id}/containers, POST connect/disconnect.
- Remove dead pages/Placeholder.tsx.

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

frontend/src/api/agents.ts

@@ -17,6 +17,10 @@ export const agentsApi = {
 
   stacks: (id: number) =>
     api.get<RemoteStackSummary[]>(`/api/agents/${id}/stacks`).then((r) => r.data),
+  createStack: (id: number, body: { name: string; yaml: string; env?: string }) =>
+    api
+      .post<{ id: string; name: string }>(`/api/agents/${id}/stacks`, body)
+      .then((r) => r.data),
   stack: (id: number, stackId: string) =>
     api.get<RemoteStackDetail>(`/api/agents/${id}/stacks/${stackId}`).then((r) => r.data),
   logs: (id: number, stackId: string, tail = 200) =>