feat: add Copy Input button for original text

[love25-codes]

Summary

Added a Copy Input button to the LinkedIn Text Formatter, allowing users to quickly copy the original input text with appropriate success and error notifications.

Related Issue

Closes #437

Changes

• Added a new Copy Input button.
• Implemented clipboard functionality to copy the contents of the input textarea.
• Reused the existing notification system to display:
  • Success message when the input text is copied.
  • Error message when attempting to copy an empty input field.
• Kept the existing Copy Output functionality unchanged.
• Maintained consistent UI styling and button placement.

Testing

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

Testing Steps

1. Enter text into the Input textarea.
2. Click Copy Input and verify that the original text is copied to the clipboard and a success notification is displayed.
3. Clear the input field, click Copy Input, and verify that an error notification ("Nothing to copy.") is shown without copying any text.

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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