feat(operations): fresh platform-operations implementation

Full rewrite of the installer (incl. the finish step), self-update pipeline,
settings store, cron webhook, dashboard/bootstrap surface, environment
manager, wizard login, config endpoint and shared helpers. Byte-compatible
public interfaces and observable behavior, including documented legacy
quirks; verified by the pilot behavioral suite and the full test suite.

app/Platform/Operations/Http/AppVersionController.php

@@ -0,0 +1,47 @@
+<?php
+
+namespace App\Platform\Operations\Http;
+
+use App\Platform\Http\Controller;
+use App\Platform\Operations\Models\Setting;
+use Illuminate\Http\JsonResponse;
+use Illuminate\Http\Request;
+use Illuminate\Support\Facades\File;
+
+/**
+ * Public probe describing the running build.
+ *
+ * Three facts, no authentication: what is on disk, which release channel the
+ * updater follows, and whether the in-app updater is available at all.
+ */
+class AppVersionController extends Controller
+{
+    /**
+     * @return JsonResponse
+     */
+    public function __invoke(Request $request)
+    {
+        return response()->json([
+            'version' => preg_replace('~[\r\n]+~', '', File::get(base_path('version.md'))),
+            'channel' => $this->releaseChannel(),
+            'containerized' => (bool) config('invoiceshelf.containerized'),
+        ]);
+    }
+
+    /**
+     * The stored channel, self-healing: the first caller to find nothing stored
+     * gets "stable" and leaves that default behind for everyone after them.
+     */
+    private function releaseChannel(): mixed
+    {
+        $stored = Setting::getSetting('updater_channel');
+
+        if (! is_null($stored)) {
+            return $stored;
+        }
+
+        Setting::setSetting('updater_channel', 'stable');
+
+        return 'stable';
+    }
+}