Relocate PDF and commitment form download logic from shortcode execution
to the `template_redirect` hook to prevent HTML output from corrupting
binary streams.
Key improvements:
- Moved download interception to `template_redirect` to ensure clean
headers and prevent partial file downloads caused by early buffer
output.
- Replaced direct `get_user_meta` calls with `IFNEX_User_Bridge::get_user_token`
to support automatic token renewal and improved authentication reliability.
- Added PDF signature validation (`%PDF` header check) to ensure
integrity of remote file responses.
- Updated Laravel base controller to include standard `AuthorizesRequests`
and `ValidatesRequests` traits.
