docs(react): document <Button> component props (#25)

[NitinSingh07]

Summary

Fixes #25

Adds comprehensive documentation and prop references for the <Button> component in @unlayer/react-elements.

Key Changes

• Detailed Props Table: Added full reference table covering children, text, href, backgroundColor, color, fontSize, fontWeight, fontFamily, padding, borderRadius, width, and textAlign, including exact default values.
• Important Type Notes: Clearly documented canonical prop shapes including fontFamily ({ label, value }), fontWeight (numeric value), href (string URL vs link object), and width="100%" for full-width layout.
• Nested Escape Hatches: Documented buttonColors, border, and the values escape hatch for advanced customization.
• Usage Examples: Added copy-pasteable snippets for common CTA buttons, mobile full-width buttons, and per-side border configurations.

Location

• Updated packages/react/README.md under Component Reference -> Button.

Verification

• pnpm build: Completed successfully.
• pnpm test: All tests passed.

[ericdellacasa8]

Thanks for picking this up! Team is reviewing the PR, will get back to you shortly!

[NitinSingh07]

Sure, I look forward to the team's review summary and suggested changes if there's any.

[ivoIturrieta]

Thanks for expanding the Button documentation. I tested the documented behavior against the latest Elements build in Chrome and found a few details to correct:

1. fontWeight also accepts "normal", "bold", "lighter", and "bolder", in addition to numbers and numeric strings.
2. textAlign also accepts "justify".
3. hoverColor and hoverBackgroundColor work in web/document output, but Button hover CSS is omitted in email mode. Please document this limitation.
4. width="100%" currently overflows in web mode when horizontal padding is present. In my browser test, the
   Button was 520px wide inside a 480px container; email mode rendered correctly at 480px. Since this is an existing implementation issue, please qualify or remove the full-width web/mobile claim rather than requiring an unrelated code fix in this PR.

The documented Arial and 400 defaults match the computed browser output and can remain.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 95.50%. Comparing base (adaa68c) to head (b118847).

Additional details and impacted files

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##             main      #50   +/-   ##
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  Coverage   95.50%   95.50%           
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  Files          31       31           
  Lines        1937     1937           
  Branches      382      382           
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  Hits         1850     1850           
  Misses         86       86           
  Partials        1        1           

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