refactor(frontend): move views into app and pages structure

Reorganize the frontend around app-level routing and page modules so the runtime and feature screens share a clearer navigation and composition layout for future work.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

frontend/src/pages/app/layout.vue

@@ -0,0 +1,29 @@
+<script setup lang="ts">
+import { RouterView } from 'vue-router'
+import SidebarNav from '@/components/SidebarNav.vue'
+</script>
+
+<template>
+  <div class="layout scanlines">
+    <SidebarNav />
+    <main class="main-content grid-bg">
+      <RouterView />
+    </main>
+  </div>
+</template>
+
+<style scoped>
+.layout {
+  display: flex;
+  height: 100vh;
+  width: 100vw;
+  background: var(--bg-void);
+  overflow: hidden;
+}
+
+.main-content {
+  flex: 1;
+  overflow: hidden;
+  position: relative;
+}
+</style>