🧹 Fix: explicit 'any' type on Window object in ModeSwitch

[kuasar-mknd]

🎯 What: The explicit 'any' type assertion on the global window object in src/components/ui/ModeSwitch.astro has been removed. The __handleThemeChange property is now explicitly typed as an extension of the Window interface in src/env.d.ts.
💡 Why: Extending the global Window interface improves codebase maintainability, type safety, and readability. It prevents TypeScript errors natively without resorting to the 'any' escape hatch, ensuring that any future references to __handleThemeChange benefit from proper IDE autocomplete and type validation.
✅ Verification: I ran formatting checks, the Astro linter/typechecker (pnpm run check), successfully built the project (pnpm run build), and successfully passed the Playwright end-to-end tests (pnpm run test:e2e).
✨ Result: The ModeSwitch component uses proper type checking on the Window object and no longer relies on explicit any bypassing.

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PR created automatically by Jules for task 5288882113611961188 started by @kuasar-mknd

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