Credit-Wallet + Ledger + Tier-Preisableitung (Fundament)

Echte Credit-Wallet (1 Credit = 1 EUR) mit append-only Ledger als Basis fuer
die Credit-Oekonomie aus dem Decision-Update (Rev. 4):

- credit_wallets (denormalisierter Saldo) + credit_transactions (Ledger,
  vorzeichenbehaftet, balance_after, polymorphe reference)
- CreditWalletService: einziger Schreibpfad, atomar mit Row-Lock,
  InsufficientCreditsException mit shortfall fuer den Mini-Checkout
- Tier-Enum (Einzel/Starter/Business/Pro/Agency) + User::currentTier()
- CreditPricingService: tier-gestaffelte Ableitung aus config/credits.php
  (Extra-PM 19/15/12/10/8, Boost 12/20/35, PDF 3, Depublish 25, Pruef-Quota)

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

app/Models/CreditTransaction.php

@@ -0,0 +1,55 @@
+<?php
+
+namespace App\Models;
+
+use App\Enums\CreditTransactionType;
+use Database\Factories\CreditTransactionFactory;
+use Illuminate\Database\Eloquent\Factories\HasFactory;
+use Illuminate\Database\Eloquent\Model;
+use Illuminate\Database\Eloquent\Relations\BelongsTo;
+use Illuminate\Database\Eloquent\Relations\MorphTo;
+
+/**
+ * Eine Zeile im Wallet-Ledger. Append-only: bestehende Buchungen werden nie
+ * verändert, Korrekturen erfolgen als Gegenbuchung (Refund).
+ */
+class CreditTransaction extends Model
+{
+    /** @use HasFactory<CreditTransactionFactory> */
+    use HasFactory;
+
+    protected $fillable = [
+        'credit_wallet_id',
+        'user_id',
+        'amount_credits',
+        'balance_after',
+        'type',
+        'description',
+        'reference_type',
+        'reference_id',
+    ];
+
+    protected function casts(): array
+    {
+        return [
+            'amount_credits' => 'integer',
+            'balance_after' => 'integer',
+            'type' => CreditTransactionType::class,
+        ];
+    }
+
+    public function wallet(): BelongsTo
+    {
+        return $this->belongsTo(CreditWallet::class, 'credit_wallet_id');
+    }
+
+    public function user(): BelongsTo
+    {
+        return $this->belongsTo(User::class);
+    }
+
+    public function reference(): MorphTo
+    {
+        return $this->morphTo();
+    }
+}

app/Models/CreditWallet.php

@@ -0,0 +1,44 @@
+<?php
+
+namespace App\Models;
+
+use App\Services\Billing\CreditWalletService;
+use Database\Factories\CreditWalletFactory;
+use Illuminate\Database\Eloquent\Factories\HasFactory;
+use Illuminate\Database\Eloquent\Model;
+use Illuminate\Database\Eloquent\Relations\BelongsTo;
+use Illuminate\Database\Eloquent\Relations\HasMany;
+
+/**
+ * Credit-Guthaben eines Users. `balance_credits` ist der denormalisierte
+ * Saldo (1 Credit = 1 €); die maßgebliche Wahrheit ist der Ledger in
+ * `transactions`. Schreibzugriffe laufen ausschließlich über
+ * {@see CreditWalletService} (atomar + gesperrt).
+ */
+class CreditWallet extends Model
+{
+    /** @use HasFactory<CreditWalletFactory> */
+    use HasFactory;
+
+    protected $fillable = [
+        'user_id',
+        'balance_credits',
+    ];
+
+    protected function casts(): array
+    {
+        return [
+            'balance_credits' => 'integer',
+        ];
+    }
+
+    public function user(): BelongsTo
+    {
+        return $this->belongsTo(User::class);
+    }
+
+    public function transactions(): HasMany
+    {
+        return $this->hasMany(CreditTransaction::class)->orderByDesc('created_at');
+    }
+}

app/Models/User.php

@@ -4,6 +4,7 @@ namespace App\Models;
 
 use App\Enums\Portal;
 use App\Enums\RegistrationType;
+use App\Enums\Tier;
 use App\Enums\UserPaymentOptionStatus;
 use Database\Factories\UserFactory;
 use Illuminate\Contracts\Auth\MustVerifyEmail;
@@ -140,6 +141,15 @@ class User extends Authenticatable implements MustVerifyEmail
             ->first();
     }
 
+    /**
+     * Abrechnungs-Tier für die Credit-Preisableitung. Ohne aktives Abo gilt
+     * `Tier::Einzel` (Pay-per-Release).
+     */
+    public function currentTier(): Tier
+    {
+        return Tier::fromPlanSlug($this->currentPlan()?->slug);
+    }
+
     /**
      * Hat dieser User ein unbegrenztes PM-Kontingent?
      *
@@ -291,6 +301,25 @@ class User extends Authenticatable implements MustVerifyEmail
         return $this->hasMany(SinglePurchase::class);
     }
 
+    public function creditWallet(): HasOne
+    {
+        return $this->hasOne(CreditWallet::class);
+    }
+
+    public function creditTransactions(): HasMany
+    {
+        return $this->hasMany(CreditTransaction::class);
+    }
+
+    /**
+     * Aktuelles Credit-Guthaben (1 Credit = 1 €). 0, solange keine Wallet
+     * angelegt wurde.
+     */
+    public function creditBalance(): int
+    {
+        return (int) ($this->creditWallet?->balance_credits ?? 0);
+    }
+
     /**
      * Lokale Rechnungen (STR- und MAN-Kreis). Überschreibt bewusst die
      * gleichnamige Cashier-Methode — Stripe-Rechnungen werden beim