Improve Leo prompt help text when a slash tool prompt is selected

[mattmcalister]

Description

Use a more relevant or descriptive help text in the prompt input box when the user has chosen to use one of the slash tool items. For example, when Change Tone > Professional is selected help text could say "Enter now or add more information"

Steps to reproduce

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Actual result

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Expected result

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Reproduces how often

Easily reproduced

Brave version (brave://version info)

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Channel information

• [X] release (stable)
• [ ] beta
• [ ] nightly

Reproducibility

• [ ] with Brave Shields disabled
• [ ] with Brave Rewards disabled
• [ ] in the latest version of Chrome

Miscellaneous information

No response

[aguscruiz]

Design idea:

• When a tool is selected, the prompt placeholder changes to Add more details to your prompt (Optional)
• On Android and iOS this requires an input box design change. The microphone icon would need to be independent of the send icon, so you can send the message without adding any sort of prompt. This could be a global change, not only for cases where tools are used.
• For cases where there isn't a tool selected, the send button should be disabled until a prompt is entered.

https://www.figma.com/design/m0Gdbf0wtqyfEFGm32VLLc/%F0%9F%94%84-Leo-%5BIN-PROGRESS%5D?node-id=1628-65072&t=gXhWRKCYuGuktxgy-1