Mito AI: Clean up chat message box

[ktaletsk]

Is your feature request related to a problem? Please describe.
Message box can have a neater design and more explicit and mouse/touch friendly UI.

Describe the solution you'd like

• Trim the extra empty space around the first input line (when the chat is empty). It does already auto-expand when more lines are added, so no need to keep the empty space pre-emptively
• Add a 'Send Message' button (possibly with a tooltip / shortcut label

Additional context
Prior Art

Chat GPT

Claude

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