fix(plugin): build the UI with devDependencies so a self-update ships its own bundle

After the 1.5.2 -> 1.5.3 self-update the server ran 1.5.3 while the dashboard
still served the 1.5.2 UI. The client build had failed, and `runtime/client-dist`
still held the previous version's bundle, so nothing looked broken — the only
signal was the Settings page's "UI build v1.5.2 (rebuild client to match)".

Cause: the whole client build toolchain (vite, typescript,
@vitejs/plugin-react, tailwindcss, @types/*) is a devDependency, and npm reads
NODE_ENV=production as --omit=dev (`NODE_ENV=production npm config get omit` ->
`dev`). The dashboard server runs with NODE_ENV=production, and every bootstrap
descended from it inherits that: the plugin-update chain, and any SessionStart
fired by a `claude` running in a tmux pane the server started. So `npm ci`
dropped vite, `tsc -b` died on missing type declarations, and buildClient
returned "failed" with the stale bundle left in place.

`--include=dev` on both install paths — a CLI flag outranks the env, which is
the point. Verified by running buildClient with NODE_ENV=production against the
installed plugin root: previously "failed", now "built", and the served bundle
carries 1.5.3.

Also: plugin-update-helper writes its verdict BEFORE the bootstrap handover as
well as after. That step retires the process tree the helper hangs off, and the
observed run reached the new server with no verdict file at all — the dashboard
reported `last_plugin_update: null` for an update that had actually succeeded.

ARCHITECTURE.md

@@ -2138,6 +2138,7 @@ The same shape is used by `GET /status`, `POST /check`, and the `update_status`
 | Newer release, ordinary checkout | `{update_available:true, situation:"release_available", latest_release:"vX.Y.Z", manual_command:"...git fetch origin --tags && git merge --ff-only vX.Y.Z..."}` | Modal opens titled with the release version, links its notes, and shows **Update now**. |
 | Newer release, plugin-cache install | `{update_available:true, situation:"plugin_managed", install_kind:"plugin", plugin_marketplace:"sg", plugin_name:"agenthub", manual_command:"claude plugin marketplace update sg && ..."}` | Modal opens WITH **Update now**; `POST /apply` answers `200 {applied:true, mode:"plugin"}` and the detached chain pulls the new version and re-bootstraps. The modal notes that an already-open Claude Code session still needs `/reload-plugins` for new skills/commands. |
 | Plugin chain ran but nothing was published | `{last_plugin_update:{ok:true, step:"already_current"}}` | The old server keeps running, untouched; no restart, no error banner. |
+| Plugin chain mid-handover | `{last_plugin_update:{ok:true, step:"bootstrap", note:"the new plugin version is installed; the server is being handed over"}}` | Written BEFORE the handover on purpose: that step retires the process tree the helper hangs off, and a helper killed there would otherwise leave `last_plugin_update: null` for an update that succeeded. Overwritten by `done` when the helper survives. |
 | Plugin chain failed (no `claude` on PATH, `npm ci` broke, bootstrap died) | `{last_plugin_update:{ok:false, step:"resolve_claude"\|"plugin_update"\|"bootstrap", error:"..."}}` | Danger banner in the modal naming the failed step. A `bootstrap` failure means the old server was already stopped, so the verdict says to run `/agenthub-update` to recover — and it is read back by whichever server comes up next, because it lives outside the cache. |
 | Plugin `/apply` with nothing newer published | 409 `{reason:"plugin_managed", release_check:"ok"}` | No chain is spawned. Message names the newest release and points at `/agenthub-update` to force a refresh. |
 | Plugin `/apply` after a failed release check | 409 `{reason:"plugin_managed", release_check:"unreachable"\|"no_local_version"\|...}` | No chain is spawned, and the message says the check did not succeed rather than claiming nothing newer exists — an unknown reported as a negative is how a broken check looks identical to an up-to-date install. |