press-releases: Publish-Rechte, Quota-Races & Slug vereinheitlichen

- Publish/Reject/Archive und changeStatus erzwingen konsistent
  press-releases:publish; changeStatus schloss die Lücke, über die das
  Status-Modal die Prüfung umging (Fix#1/H2).
- publish()/changeStatusFromAdmin sperren PM- und User-Zeile
  transaktional; QuotaExceededException wird in Admin-Publish und im
  Auto-Publish-Job abgefangen (Warnung statt 500 / bleibt in Review, Fix#3/M2).
- Slug-Erzeugung nur noch über HasUniqueSlug (generateUniqueSlug +
  saveWithUniqueSlugRetry), redundanter Controller-Helper entfernt (M3).
- API-/Legacy-Text wird vor der Persistenz sanitisiert (M6);
  Scheduler/Legacy-Tracking ignorieren soft-gelöschte PMs.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

database/migrations/2026_07_14_125841_add_scheduled_publication_index_to_press_releases_table.php

@@ -0,0 +1,31 @@
+<?php
+
+use Illuminate\Database\Migrations\Migration;
+use Illuminate\Database\Schema\Blueprint;
+use Illuminate\Support\Facades\Schema;
+
+return new class extends Migration
+{
+    /**
+     * Run the migrations.
+     */
+    public function up(): void
+    {
+        Schema::table('press_releases', function (Blueprint $table) {
+            $table->index(
+                ['status', 'classification', 'deleted_at', 'scheduled_at'],
+                'press_releases_scheduled_publication_idx',
+            );
+        });
+    }
+
+    /**
+     * Reverse the migrations.
+     */
+    public function down(): void
+    {
+        Schema::table('press_releases', function (Blueprint $table) {
+            $table->dropIndex('press_releases_scheduled_publication_idx');
+        });
+    }
+};