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/context.ts

@@ -0,0 +1,20 @@
+import type { Ref } from 'vue';
+import { useContextFactory } from '@robonen/vue';
+
+export interface NumberFieldContext {
+  value: Ref<number | null>;
+  min: Ref<number | undefined>;
+  max: Ref<number | undefined>;
+  step: Ref<number>;
+  disabled: Ref<boolean>;
+  readonly: Ref<boolean>;
+  increment: (delta?: number) => void;
+  decrement: (delta?: number) => void;
+  setValue: (v: number | null) => void;
+  inputId: string;
+}
+
+const ctx = useContextFactory<NumberFieldContext>('NumberFieldContext');
+
+export const provideNumberFieldContext = ctx.provide;
+export const useNumberFieldContext = ctx.inject;