Add mass actions to bulk update/close project tasks (progress, start date, deadline)

[mapiolca]

Motivation

• Provide mass-action support to update progress, start date, deadline and to close multiple project tasks at once from task lists and project pages.

Description

• Render a modal UI for pre-massactions in core/tpl/massactions_pre.tpl.php with per-task inputs (progress or datetime + keep-duration) and client-side logic to size the dialog and apply a global datetime to all rows.
• Add language keys in langs/en_US/projects.lang used by the new mass-action UI and result messages.
• Add Task::getAuthorizedTasksForMassAction in projet/class/task.class.php to fetch and filter selected task rows by user/project permissions and entity.
• Implement server-side handling in projet/tasks.php and projet/tasks/list.php to resolve the effective mass action, validate inputs, update tasks inside a DB transaction, handle errors, set user messages, and emit syslog traces; and register the new mass-action options in task list selectors.

Testing

• No automated tests were added for this change and no existing automated test suites were modified or executed as part of this PR.