Fase 2: read-only user role with per-category view toggles

Adds a third account type 'user' alongside super/admin: no create/edit/delete
rights on qr codes, view access to dynamic/static lists gated per-account by
two admin-controlled toggles (can_view_static, can_view_dynamic), and always
full visibility into the dashboard/reports regardless of those toggles.

- New columns can_view_static/can_view_dynamic on users (migrations/003)
- Users class + form_users.php: 'user' type option with the two toggles
- Access control: dynamic_qrcode.php/static_qrcode.php/bulk_action.php reject
  all mutations for type=user; dynamic_qrcodes.php/static_qrcodes.php enforce
  the view toggle and show all codes (no owner scoping, since 'user' owns none)
- Sidebar and list tables hide add/edit/delete/bulk UI for the read-only role
- index.php dashboard stats are unscoped for both 'super' and 'user'

db/migrations/003_user_role.sql

@@ -0,0 +1,22 @@
+-- Fase 2: read-only 'user' rol met twee zichtbaarheids-toggles.
+-- type='user' vereist geen schemawijziging (varchar(10), geen enum-constraint).
+
+SET @db := DATABASE();
+
+SET @col_exists := (
+  SELECT COUNT(*) FROM information_schema.COLUMNS
+  WHERE TABLE_SCHEMA = @db AND TABLE_NAME = 'users' AND COLUMN_NAME = 'can_view_static'
+);
+SET @sql := IF(@col_exists = 0,
+  'ALTER TABLE `users` ADD COLUMN `can_view_static` TINYINT(1) NOT NULL DEFAULT 0',
+  'SELECT 1');
+PREPARE stmt FROM @sql; EXECUTE stmt; DEALLOCATE PREPARE stmt;
+
+SET @col_exists := (
+  SELECT COUNT(*) FROM information_schema.COLUMNS
+  WHERE TABLE_SCHEMA = @db AND TABLE_NAME = 'users' AND COLUMN_NAME = 'can_view_dynamic'
+);
+SET @sql := IF(@col_exists = 0,
+  'ALTER TABLE `users` ADD COLUMN `can_view_dynamic` TINYINT(1) NOT NULL DEFAULT 0',
+  'SELECT 1');
+PREPARE stmt FROM @sql; EXECUTE stmt; DEALLOCATE PREPARE stmt;