feat: Support multiple boards on the same page

[georgylobko]

Description

Support multiple boards on one page.
AWSUI-62123

Related links, issue #, if available: n/a

How has this been tested?

Review checklist

The following items are to be evaluated by the author(s) and the reviewer(s).

Correctness

• Changes include appropriate documentation updates.
• Changes are backward-compatible if not indicated, see CONTRIBUTING.md.
• Changes do not include unsupported browser features, see CONTRIBUTING.md.
• Changes were manually tested for accessibility, see accessibility guidelines.

Security

• If the code handles URLs: all URLs are validated through the checkSafeUrl function.

Testing

• Changes are covered with new/existing unit tests?
• Changes are covered with new/existing integration tests?

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[codecov]

Codecov Report

❌ Patch coverage is 93.54839% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 92.72%. Comparing base (d33abaf) to head (2a26cc9).

Files with missing lines	Patch %	Lines
src/board/transition.ts	33.33%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #439      +/-   ##
==========================================
+ Coverage   91.24%   92.72%   +1.48%     
==========================================
  Files          59       59              
  Lines        1724     1745      +21     
  Branches      466      440      -26     
==========================================
+ Hits         1573     1618      +45     
+ Misses        151      127      -24     

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