🧪 testing improvement: add missing tests for initWasm

[paul0728]

🎯 What: Missing tests for the initWasm function in docs/index.html were addressed.
📊 Coverage: Successfully mock fetch and initializeImageMagick to test successful state updates (like button text changes and state flag update) and failure cases (verifying error messages and console output).
✨ Result: Test coverage for initialization functionality is robustly covered using @happy-dom/jest-environment. Ensure changes are safe from regressions.

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PR created automatically by Jules for task 10930269516187643518 started by @paul0728

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