Admin-scoped user accounts, secure qr code storage, PHP 8.4 upgrade

Admin-scoped users (answers: who can create a 'user' account, only super or
also an admin within their own scope?):
- New owner_admin_id column on users (migration 004). NULL means created by
  super (company-wide, previous behavior); otherwise scoped to that admin's
  own codes.
- Users::addUser/editUser/deleteUser now allow an 'admin' session, but force
  type='user' and owner_admin_id to their own id regardless of submitted
  input. user.php/users.php open up to admins with a restricted UI (no type
  picker, listing limited to their own created users).
- New qr_compute_scope_owner_id()/qr_apply_owner_scope()/qr_has_full_visibility()
  helpers in includes/security.php, replacing the ad-hoc type==='admin' checks
  in index.php, dynamic_qrcodes.php, static_qrcodes.php and bulk_action.php.
  A 'user' account created by an admin is now scoped to that admin's codes
  instead of seeing everything company-wide.

Qr code storage hardening: images were served as plain static files under the
document root with no auth check at all. Storage now lives outside the web
root; qrcode_image.php and qrcode_zip_download.php gate access with the same
permission model as the list pages, and the bulk zip download is bound to the
session that generated it.

PHP 8.4 + chillerlan/php-qrcode 6.0.1: bumped since this is a dockerized app,
so the PHP version shipped doesn't matter to end users. Note: the 6.0.1 tag
itself only requires PHP 8.2 - the earlier "needs 8.4" read was from an
unpinned clone of master, which has since moved past the tag. Fixed along the
way, surfaced by testing on 8.4:
- The hardcoded Imagick build (an old pinned master commit, workaround for
  3.7.0 being broken on PHP 8.3+) no longer compiles on 8.4. Imagick 3.8.1 is
  now a normal stable release, so the workaround is gone.
- config.php had display_errors=On + error_reporting(E_ALL), so PHP 8.4's new
  deprecation notices got dumped straight into the response before
  session_start() could run, breaking login outright. Also an info-disclosure
  risk on its own. Now logged instead of displayed.
- MysqliDb::insertMulti() had an implicit nullable parameter, now explicit.
- includes/auth_validate.php redirected unauthenticated requests but never
  called exit(), so the rest of the script kept running.
- Dockerfile.fpm was missing both git (needed to clone chillerlan/php-qrcode)
  and the imagick extension entirely.

Also removes the unused sample qr code images that shipped in the original
repo; storage now lives outside the document root so they were never going
to be served again.

src/bulk_action.php

@@ -46,22 +46,18 @@ if ($_SERVER['REQUEST_METHOD'] === 'POST') {
 
         foreach ($params as $param) {
             $db->where('id', $param);
-            if ($_SESSION['type'] === 'admin') {
-                $db->where('id_owner', $_SESSION['user_id']);
-                $db->orWhere('id_owner', NULL, 'IS');
-            }
+            qr_apply_owner_scope($db);
             $row = $db->getOne("{$type}_qrcodes");
             if ($row !== NULL) {
-                $files[] = SAVED_QRCODE_FOLDER . $row['qrcode'];
+                $files[] = SAVED_QRCODE_DIRECTORY . $row['qrcode'];
             }
         }
 
         $zip = new ZipArchive();
-        $uniqid = uniqid();
-        $relative_dir = SAVED_QRCODE_FOLDER . 'zip/qrcodes_' . $uniqid . '.zip';
-        @unlink($relative_dir);
-        $url_path = SAVED_QRCODE_URL . 'zip/qrcodes_' . $uniqid . '.zip';
-        $zip->open($relative_dir, ZipArchive::CREATE);
+        $zip_filename = 'qrcodes_' . uniqid() . '.zip';
+        $zip_path = SAVED_QRCODE_DIRECTORY . 'zip/' . $zip_filename;
+        @unlink($zip_path);
+        $zip->open($zip_path, ZipArchive::CREATE);
 
         foreach ($files as $file) {
             $download_file = @file_get_contents($file, true);
@@ -70,10 +66,13 @@ if ($_SERVER['REQUEST_METHOD'] === 'POST') {
 
         $zip->close();
 
+        // Proof-of-generation: only this session may download this specific zip file.
+        $_SESSION['generated_zips'][] = $zip_filename;
+
         audit_log('bulk_download', $type, implode(',', $params));
 
         echo json_encode([
-            'data' => $url_path,
+            'data' => 'qrcode_zip_download.php?file=' . rawurlencode($zip_filename),
             'status' => 200
         ]);
         exit();