fix(loader): respect prefers-reduced-motion

[natemoo-re]

#101654 was regretfully merged without a (prefers-reduced-motion: reduce) check. This PR implements that check to remove CSS animations and also the JS-driven bleep animation.

[cursor]

Bug: SPA Loader Breaks Reduced Motion Accessibility

The @media (prefers-reduced-motion: reduce) CSS rule is missing from the SVG <style> block. The corresponding template file (src/sentry/templates/sentry/partial/loader.html) includes this rule to disable CSS animations for users preferring reduced motion, but static/index.ejs does not. This breaks the accessibility feature on the SPA loader path.

static/index.ejs#L55-L71

sentry/static/index.ejs

Lines 55 to 71 in f0ec402

	--stagger: 50ms;
	}
	path {
	stroke-dashoffset: 1150;
	stroke-dasharray: 1150;
	animation: draw calc(var(--duration) + (var(--i) * var(--stagger)) + (1.3s - var(--delay))) calc(var(--delay) + ((3 - var(--i)) * var(--stagger))) ease-out;
	}
	[data-index="0"] {
	stroke: #F0369A;
	}
	[data-index="1"] {
	stroke: #67C800;
	}
	[data-index="2"] {
	stroke: #7553FF;
	}
	@keyframes draw {

 

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