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/App.tsx

@@ -6,6 +6,7 @@ import { Dashboard } from "@/pages/Dashboard";
 import { Stacks } from "@/pages/Stacks";
 import { StackDetail } from "@/pages/StackDetail";
 import { StackEditor } from "@/pages/StackEditor";
+import { RemoteStackDetail } from "@/pages/RemoteStackDetail";
 import { Images } from "@/pages/Images";
 import { Templates } from "@/pages/Templates";
 import { Settings } from "@/pages/Settings";
@@ -43,6 +44,7 @@ export default function App() {
             <Route path="/stacks/new" element={<StackEditor />} />
             <Route path="/stacks/:id" element={<StackDetail />} />
             <Route path="/stacks/:id/edit" element={<StackEditor />} />
+            <Route path="/hosts/:agentId/stacks/:id" element={<RemoteStackDetail />} />
             <Route path="/networks" element={<Networks />} />
             <Route path="/images" element={<Images />} />
             <Route path="/templates" element={<Templates />} />