fix(ui): improve chat history arrows styling in placeholder text

[zanesq]

Fixes #1608

Makes the chat history keyboard shortcut indicators more visually appealing and clearer in the chat input placeholder text.

Changes:

• Updated placeholder text from '⌘↑/⌘↓' to '(⌘↑/↓ for history)'
• Made the shortcut text more descriptive and easier to understand
• Improved visual formatting with parentheses

Testing:

• Verified placeholder text displays correctly
• Confirmed linting passes
• Keyboard shortcuts continue to work as expected