Phase 5: multi-host agents (0.5.0)

- stackpilot-agent: slim token-guarded FastAPI (reuses compose_service) exposing
  stack CRUD/lifecycle/logs + system info; same image, different CMD. agent/
  Dockerfile + compose + .env.example.
- Central proxy: Agent model, agent_service (httpx ping/proxy + live status:
  online/offline/unauthorized + hostname/last_seen), routers/agents.py
  (CRUD + ping + proxied stacks/lifecycle/logs/system).
- Frontend: Settings → Remote hosts (add/check/remove, connectivity dot); Stacks
  grouped by host; remote stack detail with lifecycle, live logs, compose/.env edit.

Verified end-to-end: agent+main on a shared network — register (good/bad token),
list/create/start/logs/delete remote stacks, offline detection (502).

Remote backup destinations (SFTP/S3) deferred.

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

frontend/src/api/agents.ts

@@ -0,0 +1,30 @@
+import api from "./client";
+import type { Agent, StackDetail, StackSummary } from "@/types";
+
+export type RemoteStackSummary = StackSummary & { agent_id: number; agent_name: string };
+export type RemoteStackDetail = StackDetail & { agent_id: number; agent_name: string };
+
+export const agentsApi = {
+  list: (refresh = true) =>
+    api.get<Agent[]>(`/api/agents?refresh=${refresh}`).then((r) => r.data),
+  create: (body: { name: string; url: string; token: string }) =>
+    api.post<Agent>("/api/agents", body).then((r) => r.data),
+  update: (id: number, body: { name?: string; url?: string; token?: string }) =>
+    api.put<Agent>(`/api/agents/${id}`, body).then((r) => r.data),
+  remove: (id: number) => api.delete(`/api/agents/${id}`).then((r) => r.data),
+  ping: (id: number) =>
+    api.post<{ status: string; hostname?: string }>(`/api/agents/${id}/ping`).then((r) => r.data),
+
+  stacks: (id: number) =>
+    api.get<RemoteStackSummary[]>(`/api/agents/${id}/stacks`).then((r) => r.data),
+  stack: (id: number, stackId: string) =>
+    api.get<RemoteStackDetail>(`/api/agents/${id}/stacks/${stackId}`).then((r) => r.data),
+  logs: (id: number, stackId: string, tail = 200) =>
+    api
+      .get<{ logs: string }>(`/api/agents/${id}/stacks/${stackId}/logs?tail=${tail}`)
+      .then((r) => r.data),
+  update_stack: (id: number, stackId: string, body: { yaml?: string; env?: string }) =>
+    api.put(`/api/agents/${id}/stacks/${stackId}`, body).then((r) => r.data),
+  action: (id: number, stackId: string, action: string) =>
+    api.post(`/api/agents/${id}/stacks/${stackId}/${action}`).then((r) => r.data),
+};