feat: added history hint feature

[love25-codes]

Summary

Added a visual information banner to improve the discoverability of the Recent History feature, making first-time users aware that their last 10 conversions are automatically saved.

Related Issue

Closes #439

Changes

• Added a lightweight informational banner.
• Included a clear message informing users that their last 10 conversions are automatically saved in the Recent History section.
• Styled the banner using existing theme variables to ensure consistency with both Light and Dark modes.
• Improved the visibility of the Recent History feature without altering its existing functionality.
• Kept the UI clean and non-intrusive while enhancing the user experience for first-time visitors.

Testing

• Added/updated tests
• Tested locally (describe steps below)

Testing Steps

1. Open the LinkedIn Text Formatter in a browser and verify that the information banner is displayed above the Output section.
2. Format and copy multiple pieces of text, then confirm that the banner remains visible and the Recent History section continues recording conversions as expected.
3. Toggle between Light and Dark modes to ensure the banner styling remains readable and consistent with the application's theme.

Contributor Details

• Name: Lovepreet Kaur
• GitHub Username: @love25-codes
• Program (SSoC / GSSoC / Hacktoberfest / Other): SSoC

Checklist before requesting a review

• Code follows the project's conventions
• No secrets or .env values are committed
• I have performed a self-review of my code
• Documentation has been updated if needed
• CI passes
• Linked the related issue above

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