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-tauri/build.rs

@@ -0,0 +1,3 @@
+fn main() {
+    tauri_build::build()
+}