feat(lint): add components-v2/pages-v2 boundary zones (no back-port)

Adds three new eslint-plugin-boundaries element zones and their matrix
rows so the GUI-redesign v2 surface is structurally isolated: v1 code
cannot import from v2 (back-porting forbidden), v2 can reach the
narrow FormField/Icon bridge via the components-foundation zone, and
pages-v2 can import from components-v2. Backed by a Vitest spec
running via the ESLint Node API (node environment; happy-dom's
document object breaks the case-police resolver). Adds a placeholder
src/components-v2/shared/X.vue so the resolver can classify the
import target during the test (unresolvable imports are not boundary-
checked by the plugin).

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

apps/app/src/components-v2/shared/X.vue

@@ -0,0 +1,10 @@
+<script setup lang="ts">
+// Boundary-test placeholder — do not import in production code.
+// Exists so eslint-plugin-boundaries can resolve @/components-v2/shared/X.vue
+// in unit tests (the resolver skips unresolvable imports).
+// TODO TECH-WS-GUI-REDESIGN: replace with real shared components.
+</script>
+
+<template>
+  <div />
+</template>