ci(panel): pin pnpm to 10.25.0 via packageManager

CI runs on Node 20 with `corepack enable`, which — with no packageManager pin —
downloaded the latest pnpm (11.5.3). pnpm 11 requires Node >= 22.13 and imports
node:sqlite, so `pnpm install --frozen-lockfile` crashed with
ERR_UNKNOWN_BUILTIN_MODULE on the Node 20 runner. Pin packageManager to
pnpm@10.25.0 (the version that generated the lockfile) so Corepack uses a
deterministic, Node-20-compatible pnpm in CI, the node:22 Docker build, and
locally.

panel/package.json

@@ -2,6 +2,7 @@
   "name": "roboco-panel",
   "version": "0.2.0",
   "private": true,
+  "packageManager": "pnpm@10.25.0",
   "scripts": {
     "dev": "next dev",
     "build": "next build",