fix: change $tenant internal attribute type from VAR_INTEGER to VAR_ID

VAR_ID is adapter-aware and uses the Sequence validator, which accepts
integer strings for SQL adapters and UUID7 strings for MongoDB. This
fixes StructureException when creating collections with shared tables
on MongoDB, where tenant values are UUID7-format strings.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: abnegate

src/Database/Database.php

@@ -251,8 +251,7 @@ class Database
         ],
         [
             '$id' => '$tenant',
-            'type' => self::VAR_INTEGER,
-            //'type' => self::VAR_ID, // Inconsistency with other VAR_ID since this is an INT
+            'type' => self::VAR_ID,
             'size' => 0,
             'required' => false,
             'default' => null,

src/Database/Validator/Structure.php

@@ -52,11 +52,11 @@ class Structure extends Validator
         ],
         [
             '$id' => '$tenant',
-            'type' => Database::VAR_INTEGER, // ? VAR_ID
-            'size' => 8,
+            'type' => Database::VAR_ID,
+            'size' => 0,
             'required' => false,
             'default' => null,
-            'signed' => false,
+            'signed' => true,
             'array' => false,
             'filters' => [],
         ],