feat(primitives): media-editor components, category reorg, perf + type cleanup

Reorganize components into category folders (forms/canvas/overlays/etc.); add the
media-editor headless family (timeline, curve-editor, waveform, crop, color
picker, etc.); apply perf fixes (O(1) collection lookups, plain-object drag
state, gesture-leak teardown, shallowRef color state, rect caching) and replace
source `any` with proper types.

vue/primitives/src/canvas/compare-slider/CompareSliderBefore.vue

@@ -0,0 +1,42 @@
+<script lang="ts">
+import type { PrimitiveProps } from '../../internal/primitive';
+
+/**
+ * The base ("before") layer of the comparison — the full, unclipped content
+ * that sits underneath. Rendered inside `CompareSliderRoot` and absolutely
+ * positioned to fill it (`inset: 0`). Put the original image / view here; the
+ * `CompareSliderAfter` layer is drawn on top and clipped to reveal it.
+ */
+export interface CompareSliderBeforeProps extends PrimitiveProps {}
+</script>
+
+<script setup lang="ts">
+import { Primitive } from '../../internal/primitive';
+import { useForwardExpose } from '@robonen/vue';
+import { useCompareSliderContext } from './context';
+
+const { as = 'div' } = defineProps<CompareSliderBeforeProps>();
+const ctx = useCompareSliderContext();
+const { forwardRef } = useForwardExpose();
+
+// Stable shape: same keys in the same order for a monomorphic style object.
+const style = {
+  position: 'absolute',
+  top: '0',
+  right: '0',
+  bottom: '0',
+  left: '0',
+} as const;
+</script>
+
+<template>
+  <Primitive
+    :ref="forwardRef"
+    :as="as"
+    :style="style"
+    :data-disabled="ctx.disabled.value ? '' : undefined"
+    :data-orientation="ctx.orientation.value"
+  >
+    <slot />
+  </Primitive>
+</template>