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/tsdown.config.ts

@@ -4,7 +4,8 @@ import Vue from 'unplugin-vue/rolldown';
 
 export default defineConfig({
   ...sharedConfig,
-  entry: ['src/index.ts'],
+  tsconfig: './tsconfig.src.json',
+  entry: ['src/index.ts', 'src/*/index.ts'],
   plugins: [Vue({ isProduction: true })],
   dts: { vue: true },
   deps: {
@@ -14,12 +15,14 @@ export default defineConfig({
   inputOptions: {
     resolve: {
       alias: {
-        // We need to alias @vue/shared to its ESM build to avoid issues
-        // with tree-shaking and module resolution in Rolldown
         '@vue/shared': '@vue/shared/dist/shared.esm-bundler.js',
       },
     },
   },
+  outputOptions: {
+    ...sharedConfig.outputOptions,
+    chunkFileNames: 'shared/[name]-[hash].js',
+  },
   define: {
     __DEV__: 'false',
   },