Add premium My Case MVP

includes/ToolModels.php

@@ -0,0 +1,25 @@
+<?php
+declare(strict_types=1);
+
+require_once __DIR__ . '/FreeTier.php';
+
+/**
+ * Tier-aware model routing for tools that expose the existing engine selector.
+ *
+ * Plus/trial users get the cost-controlled Azure mini path. Pro users get the
+ * full Azure path. CaveauAI sessions keep the engine requested by their UI.
+ */
+final class ToolModels
+{
+    public static function engineForUser(int $userId, string $requestedEngine): string
+    {
+        $valid = ['azure_mini', 'azure_full', 'gpu', 'regex'];
+        $requestedEngine = in_array($requestedEngine, $valid, true) ? $requestedEngine : 'azure_mini';
+
+        if ($userId <= 0) {
+            return $requestedEngine;
+        }
+
+        return FreeTier::tier($userId) === 'pro' ? 'azure_full' : 'azure_mini';
+    }
+}