TF-3944 Apply new style for composer

[dab246]

Issue

#3944

Task Done

• Replace the "Title" label with a placeholder inside the subject input field
• Harmonize the "Send" button with the new Twake system: update its border-radius to match the rounded style used for all action buttons.
• Increase the height of the message composer to provide more space for writing, improving user comfort during text input.
• The input frame “ CC BCC reply to “should automatically close when clicking outside of it, regardless of whether it has been filled or not.

Resolved

Screen.Recording.2025-08-06.at.09.38.31.mov

[github-actions]

This PR has been deployed to https://linagora.github.io/tmail-flutter/3946.

[hoangdat]

• missing change style of Signature button into three dot with hover text

[hoangdat]

• line height maybe still not 24 px

Please describe steps to reproduce it. If you use copy & paste or drag& drop text to composer, it will not applied.

[dab246]

• missing change style of Signature button into three dot with hover text

It was implemented at other PR. Please see at #3949

[dab246]

• Auto change line-height by font-size

[dab246]

• Auto change line-height by font-size

Screen.Recording.2025-08-21.at.14.10.17.mov

[hoangdat]

• color was not applied for the whole line when we change the font size in composer

[hoangdat]

• line height was not reduced when we reduce font size

[dab246]

• color was not applied for the whole line when we change the font size in composer

We don't need to fix this, this is an html format error when tags are nested, some other mail clients also have this error like GMAIL

• line height was not reduced when we reduce font size

We will move the task change line-height = 24px to another PR. This PR only completes the tasks below.

Screen.Recording.2025-08-22.at.09.51.41.mov