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/selection/combobox/ComboboxEmpty.vue

@@ -0,0 +1,41 @@
+<script lang="ts">
+import type { PrimitiveProps } from '../../internal/primitive';
+
+/**
+ * Fallback content shown when the current search term matches no items. Renders only when
+ * the filtered count is zero, unless `always` is set.
+ */
+export interface ComboboxEmptyProps extends PrimitiveProps {
+  /** Render even when items exist but none are filtered out. */
+  always?: boolean;
+}
+</script>
+
+<script setup lang="ts">
+import { computed } from 'vue';
+
+import { useForwardExpose } from '@robonen/vue';
+import { Primitive } from '../../internal/primitive';
+import { useComboboxRootContext } from './context';
+
+const { as = 'div', always = false } = defineProps<ComboboxEmptyProps>();
+
+const { forwardRef } = useForwardExpose();
+const rootCtx = useComboboxRootContext();
+
+const shouldRender = computed(() => {
+  if (always) return true;
+  return rootCtx.filterState.value.count === 0;
+});
+</script>
+
+<template>
+  <Primitive
+    v-if="shouldRender"
+    :ref="forwardRef"
+    :as="as"
+    role="presentation"
+  >
+    <slot />
+  </Primitive>
+</template>