style: 淡薰紫 Lavender Breeze + UI修复

- 主色改淡薰紫 #8B9CF7 + 白底 清新风格
- 每个智能体卡不同淡色调
- 删除欢迎卡底部"或直接对我说"
- 运动创建/打卡接入 API
- 全项目薄荷绿→淡紫替换

health_app/lib/widgets/agent_bar.dart

@@ -43,16 +43,16 @@ class AgentBar extends ConsumerWidget {
         margin: const EdgeInsets.symmetric(horizontal: 4, vertical: 6),
         padding: const EdgeInsets.symmetric(horizontal: 14),
         decoration: BoxDecoration(
-          color: isSelected ? const Color(0xFF14B8A6) : Colors.white,
-          border: Border.all(color: const Color(0xFF14B8A6)),
+          color: isSelected ? const Color(0xFF8B9CF7) : Colors.white,
+          border: Border.all(color: const Color(0xFF8B9CF7)),
           borderRadius: BorderRadius.circular(24),
         ),
         child: Row(
           mainAxisSize: MainAxisSize.min,
           children: [
-            Icon(icon, size: 16, color: isSelected ? Colors.white : const Color(0xFF14B8A6)),
+            Icon(icon, size: 16, color: isSelected ? Colors.white : const Color(0xFF8B9CF7)),
             const SizedBox(width: 6),
-            Text(label, style: TextStyle(fontSize: 13, color: isSelected ? Colors.white : const Color(0xFF14B8A6))),
+            Text(label, style: TextStyle(fontSize: 13, color: isSelected ? Colors.white : const Color(0xFF8B9CF7))),
           ],
         ),
       ),