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/components/ModeSwitcher.vue

@@ -0,0 +1,26 @@
+<template>
+  <div class="mode-switcher">
+    <button
+      v-for="m in modes"
+      :key="m.id"
+      @click="uiMode.setMode(m.id)"
+      class="mode-switcher-btn"
+      :class="{ 'mode-switcher-btn-active': uiMode.mode === m.id }"
+    >
+      {{ m.label }}
+    </button>
+  </div>
+</template>
+
+<script setup lang="ts">
+import { useUIModeStore } from '@/stores/uiMode'
+import type { UIMode } from '@/types/api'
+
+const uiMode = useUIModeStore()
+
+const modes: { id: UIMode; label: string }[] = [
+  { id: 'easy', label: 'Easy' },
+  { id: 'gamer', label: 'Pro' },
+  { id: 'chat', label: 'Chat' },
+]
+</script>