fix(primitives): eslint/tsconfig migration, asChild refactor, type fixes

- Migrate to eslint flat config + composite tsconfig.
- Complete the asChild→as="template" refactor (remove asChild prop + :as-child
  bindings across components, matching Primitive's slot model).
- Fix test type errors and source type-safety (useGraceArea hull/point math,
  FocusScope/util ref typing).

Note: ~53 vue-tsc errors remain (HTML attr/event passthrough typing on
transparent wrapper components + a couple of duplicate-export naming
collisions) — not gated by CI (build/lint/test green); pending a
component-attribute-typing design decision.

vue/primitives/src/number-field/NumberFieldIncrement.vue

@@ -0,0 +1,33 @@
+<script lang="ts">
+import type { PrimitiveProps } from '../primitive';
+export interface NumberFieldIncrementProps extends PrimitiveProps {}
+</script>
+
+<script setup lang="ts">
+import { Primitive } from '../primitive';
+import { useForwardExpose } from '@robonen/vue';
+import { useNumberFieldContext } from './context';
+
+const { as = 'button' } = defineProps<NumberFieldIncrementProps>();
+const { forwardRef } = useForwardExpose();
+const ctx = useNumberFieldContext();
+
+function onClick() {
+  ctx.increment();
+}
+</script>
+
+<template>
+  <Primitive
+    :ref="forwardRef"
+    :as="as"
+    :type="as === 'button' ? 'button' : undefined"
+    tabindex="-1"
+    aria-hidden="true"
+    :disabled="ctx.disabled.value || ctx.readonly.value || undefined"
+    :data-disabled="(ctx.disabled.value || ctx.readonly.value) ? '' : undefined"
+    @click="onClick"
+  >
+    <slot />
+  </Primitive>
+</template>