feat: SQLite DB with migrations replaces all JSON file storage

- Add db.php with PDO singleton, migration runner, and all helper functions
- Add migrations/001_initial_schema.sql (full schema)
- Add migrations/002_import_json.php (one-time JSON → DB importer)
- Add _incl/switch_tenant.php POST endpoint for tenant/centro switching
- Update tools.auth.php: DB-backed login, cookie auth, session reload, init_active_centro()
- Update all sysadmin pages (users, centros, aularios, invitations, reset_password) to use DB
- Update aulatek/index.php, aulario.php, supercafe.php, supercafe_edit.php to use DB
- Update aulatek/comedor.php and api/comedor.php to use DB
- Update aulatek/paneldiario.php: aulario config + comedor data from DB
- Update aulatek/proyectos.php: aulario config + sharing metadata from DB
- Update club/cal.php, index.php, edit_data.php, upload/upload.php to use DB
- Update account/index.php: rich profile, tenant list, aula list, session info, permissions
- Update pre-body.php account dropdown: shows active org + inline tenant switcher
- Update DATA_STRUCTURE.md to document DB approach and migration system

Co-authored-by: naielv <109038805+naielv@users.noreply.github.com>

public_html/club/index.php

@@ -1,5 +1,6 @@
 <?php
 ini_set("display_errors", 0);
+require_once "../_incl/db.php";
 $files = glob("/DATA/club/IMG/*/");
 sort($files);
 $files = array_reverse($files);
@@ -17,7 +18,7 @@ require_once "../_incl/pre-body.php"; ?>
         <?php foreach ($files as $file) {
             $filenam = str_replace("/", "", str_replace("/DATA/club/IMG/", "", $file));
             $date = implode("/", array_reverse(explode("-", $filenam)));
-            $val = json_decode(file_get_contents($file . "data.json"), true)
+            $val = db_get_club_event($filenam);
                 ?>
 
             <li><a class="btn btn-secondary" href="cal.php?f=<?php echo $filenam; ?>"><b><?php echo $date; ?></b></a> -