feat(html): add slider element (#655)

packages/html/src/ui/slider/slider-context.ts

@@ -0,0 +1,20 @@
+import type { SliderState } from '@videojs/core';
+import type { SliderThumbProps } from '@videojs/core/dom';
+import { createContext } from '@videojs/element/context';
+
+export interface SliderContextValue {
+  /** Base slider state — children use this for data attributes and value display. */
+  state: SliderState;
+  /** Domain value at the current pointer position (e.g., seconds for time, percent for volume). */
+  pointerValue: number;
+  /** ARIA attributes for the thumb element (role, tabindex, aria-value*, etc.). */
+  thumbAttrs: Record<string, string | number | boolean | undefined>;
+  /** Keyboard and focus event handlers for the thumb element. */
+  thumbProps: SliderThumbProps;
+  /** Optional formatter for value display. Receives domain value and value type. */
+  formatValue?: ((value: number, type: 'current' | 'pointer') => string) | undefined;
+}
+
+const SLIDER_CONTEXT_KEY = Symbol('@videojs/slider');
+
+export const sliderContext = createContext<SliderContextValue>(SLIDER_CONTEXT_KEY);