feat: implement three-mode UI system (Easy / Pro / Chat)

Add switchable UI modes with conditional rendering:
- Easy mode: goal-based interface with 7 guided workflows
- Pro mode: current technical interface preserved with Quick Start Goals
- Chat mode: AIUI placeholder for future integration

New components: ModeSwitcher, EasyHome, GoalDetail wizard, Chat placeholder
New stores: uiMode (mode persistence), goals (progress tracking)
New data: goal definitions catalog, helpTree goals section
Modified: Dashboard (reactive nav), Home (mode dispatcher), Settings (mode picker),
Router (goal/chat routes), Spotlight (goal search integration)

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

neode-ui/src/views/Chat.vue

@@ -0,0 +1,29 @@
+<template>
+  <div class="flex flex-col items-center justify-center min-h-[60vh]">
+    <div class="glass-card p-12 max-w-lg w-full text-center">
+      <div class="w-16 h-16 mx-auto mb-6 rounded-full bg-white/10 flex items-center justify-center">
+        <svg class="w-8 h-8 text-white/40" fill="none" stroke="currentColor" viewBox="0 0 24 24">
+          <path stroke-linecap="round" stroke-linejoin="round" stroke-width="2" d="M8 12h.01M12 12h.01M16 12h.01M21 12c0 4.418-4.03 8-9 8a9.863 9.863 0 01-4.255-.949L3 20l1.395-3.72C3.512 15.042 3 13.574 3 12c0-4.418 4.03-8 9-8s9 3.582 9 8z" />
+        </svg>
+      </div>
+      <h2 class="text-2xl font-semibold text-white mb-2">AI Assistant</h2>
+      <p class="text-white/60 mb-8 leading-relaxed">
+        Conversational interface coming soon. Talk to your node, ask questions,
+        and manage everything through natural language.
+      </p>
+      <div class="bg-white/5 border border-white/10 rounded-xl p-4">
+        <input
+          type="text"
+          disabled
+          placeholder="What would you like to do?"
+          class="w-full bg-transparent text-white/30 outline-none placeholder-white/30 cursor-not-allowed"
+        />
+      </div>
+      <p class="text-xs text-white/30 mt-4">AIUI integration in development</p>
+    </div>
+  </div>
+</template>
+
+<script setup lang="ts">
+// Chat mode placeholder — will integrate AIUI here
+</script>