feat(messages): add form styles update header

src/plainui/jinja2/plainui/components/form_elements.html

src/plainui/jinja2/plainui/components/title.html

src/plainui/jinja2/plainui/header.html

src/plainui/jinja2/plainui/personal_message_list.html

src/plainui/jinja2/plainui/personal_message_send.html

src/plainui/styles/components/_header.scss