fix(a11y): add accessible names to hud sliders and inputs

Add explicit aria-label attributes to unlabelled interactive controls in index.html and dynamic parameter sliders in src/ui.js, fulfilling WCAG 2.1 Success Criterion 4.1.2 (Name, Role, Value).

- Add aria-label to #scope-feather-slider, #bloom-intensity-slider, #sharpen-intensity-slider, #location-search, #scene-import-file, and first-run suppression checkbox.
- Set aria-label to uniform label on dynamic style parameter sliders in ui.js.
- Add unit test suite (src/hudA11y.test.mjs) verifying accessible names across all inputs in index.html and dynamic slider construction.

Signed-off-by: Kushagra Kumar <[email protected]>

src/ui.js

@@ -8930,6 +8930,7 @@ export class StyleManager {
       const slider = document.createElement('input');
       slider.type = 'range';
       slider.className = 'param-slider';
+      slider.setAttribute('aria-label', uMeta.label);
       slider.min = uMeta.min;
       slider.max = uMeta.max;
       slider.step = uMeta.max <= 1 ? '0.01' : '0.1';