feat(gpu): GPU agent admin card — token, queue, backfill (#114)

The FC-side control surface the operator asked for: Settings → Tagging → "GPU
agent". Generate/reveal/copy/rotate the agent bearer token (with the FC URL to
point the agent at), see the live job-queue depth (pending/in-flight/done/
errored, polled), and a "Queue character embedding (CCIP)" button that triggers
the library backfill. Plain-HTTP-safe copy (copyText resolves on success,
throws on fail). Closes the "how do I get the token in the UI" gap.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Ttrj5P7upUTueSfoJcxEqa

frontend/src/stores/gpu.js

@@ -0,0 +1,33 @@
+import { defineStore } from 'pinia'
+
+import { useApi } from '../composables/useApi.js'
+
+// GPU agent control surface (#114): the FC-side admin for the desktop agent —
+// the bearer token it authenticates with, the job-queue depth, and the backfill
+// trigger. The agent itself talks to /api/gpu/jobs/* over HTTP; nothing here
+// touches Redis/Postgres directly.
+export const useGpuStore = defineStore('gpu', () => {
+  const api = useApi()
+
+  // { token: <string|null>, configured: bool }
+  async function token() {
+    return await api.get('/api/gpu/token')
+  }
+
+  // Generate a fresh token (invalidates the old one). Returns { token }.
+  async function rotateToken() {
+    return await api.post('/api/gpu/token/rotate')
+  }
+
+  // { pending, leased, done, error }
+  async function status() {
+    return await api.get('/api/gpu/status')
+  }
+
+  // Enqueue a job per image lacking one for `task` (the agent drains it).
+  async function backfill(task = 'ccip') {
+    return await api.post('/api/gpu/backfill', { body: { task } })
+  }
+
+  return { token, rotateToken, status, backfill }
+})