Fix AnimatedThemeToggler crash on Firefox (View Transitions API fallback)

[DhirajTsx]

Firefox compatibility fix for AnimatedThemeToggler

Problem

Firefox does not support the View Transitions API (document.startViewTransition),
which causes the Animated Theme Toggler to throw a runtime error and stop working.

Solution

This PR adds safe feature detection and a graceful fallback:

• Uses the animated transition when startViewTransition is available
• Falls back to an instant theme toggle on unsupported browsers (e.g. Firefox)
• Prevents crashes while preserving functionality

Result

• Chrome and supported browsers keep the animation
• Firefox and other unsupported browsers work without errors
• Improved cross-browser reliability

[vercel]

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