Add comment spam classification and captcha checks.

Score artwork comments with local signatures plus Together AI, and optionally require Turnstile before posting.

app/Models/CommentSpamSignature.php

@@ -0,0 +1,22 @@
+<?php
+
+namespace App\Models;
+
+use Illuminate\Database\Eloquent\Model;
+
+class CommentSpamSignature extends Model
+{
+    public $timestamps = false;
+
+    protected $fillable = [
+        'content_hash', 'pattern_signature', 'source', 'reason',
+        'confidence', 'hit_count', 'reviewed_by', 'metadata', 'created_at',
+    ];
+
+    protected $casts = [
+        'confidence' => 'integer',
+        'hit_count' => 'integer',
+        'metadata' => 'array',
+        'created_at' => 'datetime',
+    ];
+}