P1: sidecar lifecycle and HTTP bridge

Backend
- sidecar.rs supervises the bundled `mycelium` binary launched via
  pkexec; locates it in resource_dir or CARGO_MANIFEST_DIR/binaries
  matching $TAURI_ENV_TARGET_TRIPLE
- ephemeral port via portpicker, key + config persisted in
  app_data_dir, kill_on_drop with explicit start_kill on stop
- health-check loop calls /api/v1/admin until 2xx (timeout 20s);
  emits sidecar://ready and sidecar://exited
- 500-line ring buffer of stdout/stderr surfaced via sidecar_logs
  command for the upcoming Settings page
- elevation::is_auth_failure(126|127) maps pkexec cancel to a
  dedicated AppError variant
- AppError uses thiserror, Serialize impl renders messages as
  plain strings for the JS side

Frontend
- typed `api` wrapper around invoke() in src/lib/api.ts
- node store (Pinia) bootstraps on mount, listens on
  sidecar://ready and sidecar://exited
- StartupOverlay covers the whole window for idle/starting/error
  phases; sidebar status dot + start/stop button
- Status view renders subnet, pubkey, api endpoint and key path
  with one-click clipboard copy

src/App.vue

@@ -1,5 +1,5 @@
 <script setup lang="ts">
-import { computed } from "vue";
+import { computed, onBeforeUnmount, onMounted } from "vue";
 import { RouterLink, RouterView, useRoute } from "vue-router";
 import {
   Activity,
@@ -8,9 +8,16 @@ import {
   MessageSquare,
   Hash,
   Settings as SettingsIcon,
+  Power,
+  PowerOff,
 } from "lucide-vue-next";
+import StartupOverlay from "@/components/StartupOverlay.vue";
+import { useNodeStore } from "@/stores/node";
+import { storeToRefs } from "pinia";
 
 const route = useRoute();
+const node = useNodeStore();
+const { phase, info, error } = storeToRefs(node);
 
 const navItems = [
   { to: "/status", label: "Status", icon: Activity },
@@ -22,15 +29,48 @@ const navItems = [
 ];
 
 const currentTitle = computed(() => (route.meta?.title as string) ?? "Mycellium");
+
+onMounted(() => {
+  node.bootstrap();
+});
+
+onBeforeUnmount(() => {
+  node.dispose();
+});
+
+async function handleStart() {
+  try {
+    await node.start();
+  } catch {
+    // error already in store
+  }
+}
+
+async function handleStop() {
+  await node.stop();
+}
 </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="relative 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>
+        <span
+          class="ml-auto inline-block h-2 w-2 rounded-full"
+          :class="
+            phase === 'ready'
+              ? 'bg-emerald-500'
+              : phase === 'starting'
+              ? 'bg-yellow-500 animate-pulse'
+              : phase === 'error'
+              ? 'bg-destructive'
+              : 'bg-muted-foreground'
+          "
+          :title="phase"
+        />
       </div>
       <nav class="flex-1 overflow-y-auto px-2 py-3 space-y-1">
         <RouterLink
@@ -45,17 +85,49 @@ const currentTitle = computed(() => (route.meta?.title as string) ?? "Mycellium"
           <span>{{ item.label }}</span>
         </RouterLink>
       </nav>
+      <div
+        v-if="info"
+        class="border-t border-border px-3 py-3 text-xs space-y-1"
+      >
+        <div class="text-muted-foreground">Overlay subnet</div>
+        <div class="font-mono break-all">{{ info.nodeSubnet }}</div>
+        <button
+          class="mt-2 inline-flex w-full items-center justify-center gap-2 rounded-md border border-border px-2 py-1 text-xs hover:bg-secondary"
+          @click="handleStop"
+        >
+          <PowerOff class="h-3 w-3" />
+          Stop daemon
+        </button>
+      </div>
+      <div
+        v-else-if="phase === 'idle' || phase === 'error'"
+        class="border-t border-border px-3 py-3"
+      >
+        <button
+          class="inline-flex w-full items-center justify-center gap-2 rounded-md bg-primary px-2 py-1.5 text-xs font-medium text-primary-foreground hover:opacity-90"
+          @click="handleStart"
+        >
+          <Power class="h-3 w-3" />
+          Start daemon
+        </button>
+      </div>
     </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"
-      >
+      <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>
+
+    <StartupOverlay
+      v-if="phase !== 'ready' && phase !== 'idle'"
+      :phase="phase as 'starting' | 'error'"
+      :error="error"
+      @start="handleStart"
+      @retry="handleStart"
+    />
   </div>
 </template>