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/alert-dialog/AlertDialogContent.vue

@@ -0,0 +1,43 @@
+<script lang="ts">
+import type { DialogContentEmits, DialogContentProps } from '../dialog';
+
+export interface AlertDialogContentProps extends Omit<DialogContentProps, 'role'> {}
+export type AlertDialogContentEmits = DialogContentEmits;
+</script>
+
+<script setup lang="ts">
+import { DialogContent } from '../dialog';
+
+const props = defineProps<AlertDialogContentProps>();
+const emit = defineEmits<AlertDialogContentEmits>();
+
+function onOpenAutoFocus(event: Event) {
+  emit('openAutoFocus', event);
+  if (event.defaultPrevented) return;
+  queueMicrotask(() => {
+    const content = document.querySelector<HTMLElement>('[data-alert-dialog-content]');
+    const cancel = content?.querySelector<HTMLElement>('[data-alert-dialog-cancel]');
+    if (cancel) {
+      event.preventDefault();
+      cancel.focus();
+    }
+  });
+}
+</script>
+
+<template>
+  <DialogContent
+    v-bind="props"
+    role="alertdialog"
+    data-alert-dialog-content
+    @open-auto-focus="onOpenAutoFocus"
+    @close-auto-focus="emit('closeAutoFocus', $event)"
+    @escape-key-down="emit('escapeKeyDown', $event)"
+    @pointer-down-outside="(e: PointerEvent | MouseEvent) => { e.preventDefault(); emit('pointerDownOutside', e); }"
+    @focus-outside="(e: FocusEvent) => { e.preventDefault(); emit('focusOutside', e); }"
+    @interact-outside="emit('interactOutside', $event)"
+    @dismiss="emit('dismiss')"
+  >
+    <slot />
+  </DialogContent>
+</template>