refactor: replace lz-string with native CompressionStream API

[magnus-madsen]

Summary

• Replace the lz-string library with the browser-native CompressionStream/DecompressionStream API (DEFLATE-raw + base64url encoding), removing the dependency entirely
• Move compression from every-keystroke to on-demand when "Shareable Link" is clicked (async)
• Clear the ?q= query param from the URL when the user edits code or selects a sample from the dropdown

Test plan

• npm run build succeeds with no lz-string references
• Load app with no query param — default program loads
• Edit code or select a dropdown example — ?q= is removed from URL if present
• Click "Shareable Link" — URL updates with compressed ?q= param
• Copy that URL and open in a new tab — program loads correctly
• Confirm lz-string is gone from package.json and node_modules

Note: Existing shared URLs using the old lz-string format will no longer decode. If backwards compatibility is needed, a fallback decoder can be added.

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