refactor: split API routes into separate files

Reorganize routes following design-to-pack pattern:
- routes/markers.php: CRUD operations for markers
- routes/position.php: Position update (single mode)
- routes/image.php: Image capture and regeneration flag management

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

public/site/plugins/map-editor/index.php

@@ -50,7 +50,11 @@ Kirby::plugin('geoproject/map-editor', [
         ]
     ],
     'api' => [
-        'routes' => require __DIR__ . '/api/routes.php'
+        'routes' => [
+            require __DIR__ . '/routes/markers.php',
+            require __DIR__ . '/routes/position.php',
+            require __DIR__ . '/routes/image.php',
+        ]
     ],
     'hooks' => [
         'page.update:after' => function ($newPage, $oldPage) {