fix: add noreferrer to external GitHub link

[charu2210]

Summary

Adds the missing noreferrer value to an external GitHub link opened with target="_blank" in the landing page.

Closes #262

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Type of Change

• Bug fix
• New feature
• Refactor (no functional change)
• UI / Design change
• Tests only
• Documentation
• Infrastructure / DevOps
• Security

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What Changed

• Updated the external GitHub link in apps/web/src/routes/+page.svelte
• Added rel="noreferrer" alongside noopener
• Improved external link security best practices for links opened in new tabs

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How to Test

1. Run the application locally using pnpm dev
2. Open the landing page
3. Click the GitHub button and verify it opens securely in a new tab

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Checklist

• My code follows the project's coding style (pnpm -r run lint passes).
• TypeScript compiles without errors (pnpm -r run typecheck).
• I have added or updated tests for the changes I made.
• All tests pass locally (pnpm -r run test).
• I have updated documentation where necessary.
• No new console.log or debug statements left in the code.
• Breaking changes are documented in this PR description.

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Additional Context

This PR addresses a remaining external link that used target="_blank" without the complete recommended rel="noopener noreferrer" configuration.