feat(updates): detect the newest release and self-apply it, including plugin installs

Update detection was a commit count against the default branch, which says nothing about whether a *version* shipped and is pure noise on the plugin cache (a depth-1 clone, where every distance is a graft artefact). It now reads the forge's own releases API and compares the published tag to this install's package.json version, falling back to the commit count only when no release can be read — with the reason in release_check, so "up to date" never silently means "we could not look".

Two states a commit count cannot express: dev_build (ahead of the newest release, missing nothing from it) now reads "Dev build - N ahead" instead of a false "Up to date"; and on a shallow clone every commits_*_release field is null and dev_build is never asserted, because the numbers would be meaningless.

POST /api/updates/apply gains a second mode, chosen by install kind and never by the request body. A checkout still fast-forwards onto the release tag, rebuilds and self-restarts. A ~/.claude/plugins/cache/ install is refused by applyUpdate (that directory is Claude Code's to replace) and handed instead to a detached chain: claude plugin marketplace update -> claude plugin update -y -> plugin-bootstrap.js --force from the NEW cache dir, which retires this server and starts its replacement. Both write the HTTP response before anything stops the process.

The chain records every outcome to plugin-update.json in the runtime dir, outside the cache the update replaces, so the next server reports it as last_plugin_update: a failed chain is otherwise indistinguishable from a slow one, and the tab would poll a server that never returns. /reload-plugins is deliberately not in the chain - it is REPL-scoped to the session that runs it, so no background process can perform it, and plugin-bootstrap derives PLUGIN_ROOT from its own __dirname, which is what makes it unnecessary for the dashboard.

Also rebrands the sidebar subtitle, splash and page title to SmartGift Solution, and corrects three ARCHITECTURE.md statements that claimed /apply did not exist.

Verified: server 1683/1683, client 486/486, build, prettier, file-header audit, openapi.yaml regenerated.

bin/agenthub.js

@@ -1190,7 +1190,7 @@ async function cmdPricing(flags, positional) {
 // ── Updates ─────────────────────────────────────────────────────────────────
 
 async function cmdUpdateCheck() {
-  console.log(c.dim("Checking the canonical remote — this can take a few seconds…"));
+  console.log(c.dim("Checking the repository's latest release — this can take a few seconds…"));
   // POST /check (rather than GET /status) so a dashboard open in the browser
   // sees the same fresh result via the update_status websocket broadcast.
   const s = await post("/api/updates/check");
@@ -1203,6 +1203,13 @@ async function cmdUpdateCheck() {
     console.log(`${c.yellow("!")}  ${s.message} ${c.dim(`(${s.fetch_error})`)}`);
     return;
   }
+  // Say WHY the release lookup produced nothing, so a green "up to date" is
+  // never mistaken for "the release list was actually read".
+  if (s.release_check && s.release_check !== "ok") {
+    console.log(
+      c.dim(`   could not read the latest release (${s.release_check}) — compared commits instead`)
+    );
+  }
   if (s.update_available) {
     console.log(`${c.yellow("⬆")}  ${s.message}`);
     if (s.situation_note) console.log(c.dim(`   ${s.situation_note}`));
@@ -2990,7 +2997,7 @@ const COMMAND_GROUPS = [
       ["export", "[file.json]", "Export all data as JSON"],
       ["cleanup", "--hours N --days M", "Abandon stale / purge old sessions"],
       ["reinstall-hooks", "", "Reinstall Claude Code hooks"],
-      ["update-check", "", "Check whether the dashboard checkout is behind upstream"],
+      ["update-check", "", "Check whether a newer release of the dashboard was published"],
       ["clear-data", "--yes", "Delete ALL data (requires --yes)"],
       ["open", "", "Open the dashboard in your browser"],
       ["version", "", "Print the agenthub version (also: --version, -v)"],
@@ -3254,7 +3261,8 @@ const SERVER_ONLY_REASONS = {
   cleanup: "cleanup is a server-side mutation",
   "clear-data": "data wipes must go through the server",
   "reinstall-hooks": "hook installation is performed by the server",
-  "update-check": "the update check runs server-side (git fetch against the canonical remote)",
+  "update-check":
+    "the update check runs server-side (reads the repo's latest release, git fetch as fallback)",
   info: "system info (uptime, memory, WS connections) only exists on a running server",
   health: "health is, by definition, a check against the running server",
 };