[Improve] Simplify Fast response mode settings copy

[roomote-roomote]

​Opened on behalf of @mrubens. Follow up by mentioning @roomote-roomote, in the web UI, or in Slack.

What changed

• Simplified the Personal Settings description for Fast response mode.
• Updated the focused component test to assert the new copy.
• Kept the detailed Personal Settings and provider documentation unchanged because its platform-specific behavior remains accurate and useful.

Why this change was made

The settings toggle should explain its default behavior concisely without carrying detailed platform caveats in the UI.

Impact

Users see a shorter Fast response mode description covering homepage prompts and linked chat messages. Detailed precedence, supported-surface, and explicit Slack behavior remain documented.

[roomote-community]

1 issue outstanding. See task

• apps/web/src/components/settings/UserPreferencesSection.tsx:143 Broad “linked chat messages” copy implies unsupported providers also use Fast mode.

_{Reviewed 72c739f}

[roomote-community]

linked chat messages now implies the setting applies to every linked chat provider, but the preference is only consumed for linked Slack and Discord accounts; GitHub, Teams, and Telegram are excluded. This can set incorrect expectations for linked Teams or Telegram users. Keep the shorter copy while naming the supported providers.

Suggested change

	Use fast responses by default for homepage prompts and linked chat
	messages.
	Use fast responses by default for homepage prompts and messages from linked Slack and Discord accounts.