feat(v5): gate V5 to development environments only

Introduce V5Feature and config so V5 routes, jobs, commands, morph maps,
and model queries run only when enabled. Move V5 migrations to
migrations-v5 (loaded only when enabled), remove Flux from production
Docker/install paths, and add isolation tests.

routes/api.php

@@ -9,6 +9,7 @@ use App\Http\Controllers\Api\DigitalOceanController;
 use App\Http\Controllers\Api\GithubController;
 use App\Http\Controllers\Api\HetznerController;
 use App\Http\Controllers\Api\Internal\FluxResourceStatusController;
+use App\Support\V5\V5Feature;
 use App\Http\Controllers\Api\OtherController;
 use App\Http\Controllers\Api\ProjectController;
 use App\Http\Controllers\Api\ResourcesController;
@@ -287,7 +288,10 @@ Route::group([
 Route::group([
     'prefix' => 'v1',
 ], function () {
-    Route::post('/internal/flux/resource-status', FluxResourceStatusController::class);
+    if (V5Feature::enabled()) {
+        Route::post('/internal/flux/resource-status', FluxResourceStatusController::class);
+    }
+
     Route::post('/sentinel/push', [SentinelController::class, 'push']);
 });