fix: resolve hydration mismatch on sample load and format block names

[madawei2699]

Resolves #25. Removes direct window.location access, moves query param loading to useEffect, and replaces underscores in block ID names.

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[gemini-code-assist]

Code Review

This pull request refactors the playground page by removing synchronous sample loading from initial state initializers and deferring it to a useEffect hook. It also updates the block composition display to replace underscores with spaces. The review feedback highlights a potential memory leak and race condition in the asynchronous sample loading hook due to an uncleared setTimeout, and suggests simplifying the block name formatting logic using a regular expression.

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