🧹 Code Health: Remove explicit 'any' from Lightbox.astro

[kuasar-mknd]

🎯 What:
Removed window as any cast and added strict typings for the custom properties attached to the global Window object used by the Lightbox component.

💡 Why:
Using any disables TypeScript's type checking, making the codebase more prone to errors and harder to refactor. Extending the global Window interface improves code maintainability and enforces strict types throughout the Astro components.

✅ Verification:
Ran pnpm run check (formatter, linter, typecheck). All passing without any explicit any warnings. Ran the full E2E test suite with Playwright and all 7 tests passed (including the Lightbox specific tests).

✨ Result:
Cleaner, strictly typed code without any casts or eslint-disable comments.

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PR created automatically by Jules for task 5764700744994571687 started by @kuasar-mknd

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