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/menus/menubar/MenubarSeparator.vue

@@ -0,0 +1,19 @@
+<script lang="ts">
+import type { MenuSeparatorProps } from '../menu';
+
+/**
+ * A horizontal divider used to visually separate groups of items within a menu.
+ * Decorative and skipped by keyboard navigation.
+ */
+export interface MenubarSeparatorProps extends MenuSeparatorProps {}
+</script>
+
+<script setup lang="ts">
+import { MenuSeparator } from '../menu';
+
+const props = defineProps<MenubarSeparatorProps>();
+</script>
+
+<template>
+  <MenuSeparator v-bind="props"><slot /></MenuSeparator>
+</template>