feat: 长辈模式（大字大按钮 + 偏好按账号隔离）+ 语音输入（按住说话 + 实时转写 + 后端代理 DashScope ASR + 患者端专用）+ 健康仪表盘背景渐变

health_app/lib/core/app_theme.dart

@@ -776,6 +776,74 @@ class AppTheme {
     ),
   );
 
+  /// 长辈模式只在已登录的患者端启用。这里提高主题级控件尺寸，页面中写死的
+  /// 字号再由 ElderModeScope 提供的文本缩放统一兜底。
+  static ThemeData get elderLightTheme {
+    final base = lightTheme;
+    return base.copyWith(
+      appBarTheme: base.appBarTheme.copyWith(
+        toolbarHeight: 60,
+        titleTextStyle: const TextStyle(
+          fontSize: 24,
+          fontWeight: FontWeight.w700,
+          color: text,
+        ),
+        iconTheme: const IconThemeData(size: 28, color: text),
+      ),
+      textTheme: base.textTheme.copyWith(
+        headlineLarge: const TextStyle(
+          fontSize: 28,
+          fontWeight: FontWeight.w700,
+          color: text,
+        ),
+        titleLarge: const TextStyle(
+          fontSize: 22,
+          fontWeight: FontWeight.w700,
+          color: text,
+        ),
+        titleMedium: const TextStyle(
+          fontSize: 19,
+          fontWeight: FontWeight.w600,
+          color: text,
+        ),
+        bodyLarge: const TextStyle(fontSize: 18, color: text, height: 1.5),
+        bodyMedium: const TextStyle(fontSize: 16, color: textSub, height: 1.45),
+        labelMedium: const TextStyle(fontSize: 16, color: textSub),
+        labelSmall: const TextStyle(fontSize: 15, color: textHint),
+      ),
+      inputDecorationTheme: base.inputDecorationTheme.copyWith(
+        contentPadding: const EdgeInsets.symmetric(
+          horizontal: 18,
+          vertical: 16,
+        ),
+        hintStyle: const TextStyle(color: textHint, fontSize: 17),
+      ),
+      elevatedButtonTheme: ElevatedButtonThemeData(
+        style: ElevatedButton.styleFrom(
+          backgroundColor: primary,
+          foregroundColor: Colors.white,
+          minimumSize: const Size(double.infinity, 56),
+          shape: RoundedRectangleBorder(
+            borderRadius: BorderRadius.circular(rLg),
+          ),
+          textStyle: const TextStyle(fontSize: 18, fontWeight: FontWeight.w700),
+          elevation: 0,
+        ),
+      ),
+      outlinedButtonTheme: OutlinedButtonThemeData(
+        style: OutlinedButton.styleFrom(
+          foregroundColor: text,
+          minimumSize: const Size(52, 56),
+          side: const BorderSide(color: border),
+          shape: RoundedRectangleBorder(
+            borderRadius: BorderRadius.circular(rMd),
+          ),
+          textStyle: const TextStyle(fontSize: 18, fontWeight: FontWeight.w700),
+        ),
+      ),
+    );
+  }
+
   static ShadThemeData get shadTheme => ShadThemeData(
     brightness: Brightness.light,
     colorScheme: ShadVioletColorScheme.light(