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.

app/Providers/RouteServiceProvider.php

@@ -2,6 +2,7 @@
 
 namespace App\Providers;
 
+use App\Support\V5\V5Feature;
 use Illuminate\Cache\RateLimiting\Limit;
 use Illuminate\Foundation\Support\Providers\RouteServiceProvider as ServiceProvider;
 use Illuminate\Http\Request;
@@ -34,10 +35,12 @@ class RouteServiceProvider extends ServiceProvider
             Route::prefix('webhooks')
                 ->group(base_path('routes/webhooks.php'));
 
-            Route::middleware('v5.web')
-                ->prefix('v5')
-                ->as('v5.')
-                ->group(base_path('routes/v5.php'));
+            if (V5Feature::enabled()) {
+                Route::middleware('v5.web')
+                    ->prefix('v5')
+                    ->as('v5.')
+                    ->group(base_path('routes/v5.php'));
+            }
 
             Route::middleware('web')
                 ->group(base_path('routes/web.php'));
@@ -60,13 +63,11 @@ class RouteServiceProvider extends ServiceProvider
             return Limit::perMinute(5)->by($request->user()?->id ?: $request->ip());
         });
 
-        // v5 authenticated web endpoints run synchronous SSH/Flux work per
-        // request (connectivity checks, bootstrap, diagnostics). Throttle per
-        // user so a single member cannot pin FPM workers by hammering them,
-        // while leaving ample headroom for the canvas's 3s cluster polling.
-        RateLimiter::for('v5', function (Request $request) {
-            return Limit::perMinute(120)->by($request->user()?->id ?: $request->ip());
-        });
+        if (V5Feature::enabled()) {
+            RateLimiter::for('v5', function (Request $request) {
+                return Limit::perMinute(120)->by($request->user()?->id ?: $request->ip());
+            });
+        }
 
         RateLimiter::for('feedback', function (Request $request) {
             return Limit::perMinute(3)->by($request->user()?->id ?: $request->ip());