fix(api): an RPC that returns a number no longer crashes the request

award_coins answers the new balance; json_decode gave an int and
SupabaseClient::request(), typed to return an array, threw a TypeError.
Every achievement that paid coins answered 500 after the coins were
already granted (seen in production on achievements.php). Scalars now
come back as ['result' => value]; error bodies that are not objects no
longer index into a scalar.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

config/database.php

@@ -109,8 +109,13 @@ class SupabaseClient {
 
         $decoded = json_decode($response, true);
         if ($httpCode >= 400) {
-            return ['error' => $decoded['message'] ?? $decoded['error'] ?? 'Request failed', 'code' => $httpCode];
+            $msg = is_array($decoded) ? ($decoded['message'] ?? $decoded['error'] ?? null) : null;
+            return ['error' => $msg ?? 'Request failed', 'code' => $httpCode];
         }
+        // An RPC that returns a scalar (award_coins answers the new balance)
+        // decodes to an int or a string; the return type is an array, so a bare
+        // value threw a TypeError and the whole request answered 500.
+        if ($decoded !== null && !is_array($decoded)) return ['result' => $decoded];
         return $decoded ?? [];
     }
 }