feat(button): add subtle active pressed state (scale + brightness)

[Abhishek6969-69]

Summary
Adds a subtle :active (pressed) state to the shared Button component to improve click/tap feedback. The effect is a slight scale down (0.98) plus a tiny brightness reduction. Reduced-motion users are respected.

Why
Improves perceived responsiveness, especially on mobile/touch devices, and aligns the component with common UX patterns.

Implementation

• Added active:scale-[0.98] active:brightness-95 motion-reduce:active:scale-100 to the button base class in Button component.

Testing checklist

• Click a primary button on desktop: see slight scale-down + darker look while mouse is pressed.
• Tap a button on mobile: tactile visual feedback appears (scale + brightness).
• Verify hover styles remain unchanged.
• Verify disabled buttons show no active feedback.
• Turn on OS Reduce Motion and verify there is no scale animation.
• Keyboard focus via Tab still shows the correct focus-visible ring.
• Visual regression / Storybook checks if applicable.

Notes
If maintainers prefer variant-specific styling instead of a global default, I can adjust in a follow-up.

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