P0: scaffold Vite + Vue 3 + Tauri v2

- pnpm + TS + Tailwind 3 + Pinia + Vue Router with hash history
- 6 placeholder views (Status, Peers, Routes, Messages, Topics, Settings)
  rendered via lucide-icon sidebar in App.vue
- Tauri v2: shell, store, log, dialog plugins; bundle targets deb +
  appimage; sidecar wired via externalBin = binaries/mycelium
- scripts/fetch-mycelium.sh pins v0.6.1, maps musl asset onto
  gnu target triple expected by Tauri bundler
- CI: pnpm typecheck + cargo fmt/clippy/test

src/App.vue

@@ -0,0 +1,61 @@
+<script setup lang="ts">
+import { computed } from "vue";
+import { RouterLink, RouterView, useRoute } from "vue-router";
+import {
+  Activity,
+  Users,
+  Route as RouteIcon,
+  MessageSquare,
+  Hash,
+  Settings as SettingsIcon,
+} from "lucide-vue-next";
+
+const route = useRoute();
+
+const navItems = [
+  { to: "/status", label: "Status", icon: Activity },
+  { to: "/peers", label: "Peers", icon: Users },
+  { to: "/routes", label: "Routes", icon: RouteIcon },
+  { to: "/messages", label: "Messages", icon: MessageSquare },
+  { to: "/topics", label: "Topics", icon: Hash },
+  { to: "/settings", label: "Settings", icon: SettingsIcon },
+];
+
+const currentTitle = computed(() => (route.meta?.title as string) ?? "Mycellium");
+</script>
+
+<template>
+  <div class="flex h-screen w-screen overflow-hidden bg-background text-foreground">
+    <aside
+      class="flex w-56 shrink-0 flex-col border-r border-border bg-card"
+    >
+      <div class="flex h-14 items-center px-4 border-b border-border">
+        <span class="font-semibold text-base">Mycellium</span>
+      </div>
+      <nav class="flex-1 overflow-y-auto px-2 py-3 space-y-1">
+        <RouterLink
+          v-for="item in navItems"
+          :key="item.to"
+          :to="item.to"
+          class="flex items-center gap-3 rounded-md px-3 py-2 text-sm transition-colors"
+          active-class="bg-secondary text-secondary-foreground"
+          exact-active-class="bg-secondary text-secondary-foreground"
+        >
+          <component :is="item.icon" class="h-4 w-4" />
+          <span>{{ item.label }}</span>
+        </RouterLink>
+      </nav>
+    </aside>
+
+    <main class="flex flex-1 flex-col overflow-hidden">
+      <header
+        class="flex h-14 items-center border-b border-border px-6 shrink-0"
+      >
+        <h1 class="text-lg font-semibold">{{ currentTitle }}</h1>
+      </header>
+      <div class="flex-1 overflow-y-auto p-6">
+        <RouterView />
+      </div>
+    </main>
+  </div>
+</template>