feat(mp): Phase 2 功能补全 — SOS+推送+趋势图tooltip+家属安全存储

- index: 添加 SOS 紧急求助悬浮按钮（仅患者可见）
- alerts: 告警页面添加微信推送订阅 + critical 推送标识
- TrendChart: 添加触摸 tooltip 显示日期和数值
- family: edit_patient 改用 secureSet/secureGet 安全存储

apps/miniprogram/src/pages/index/index.scss

@@ -499,3 +499,43 @@
   font-weight: 600;
   color: $white;
 }
+
+// ── SOS 紧急求助按钮 ──
+
+.sos-btn {
+  position: fixed;
+  right: 24px;
+  bottom: 140px;
+  width: 56px;
+  height: 56px;
+  border-radius: 50%;
+  background: #DC2626;
+  display: flex;
+  align-items: center;
+  justify-content: center;
+  box-shadow: 0 4px 12px rgba(220, 38, 38, 0.4);
+  z-index: 100;
+
+  &:active {
+    opacity: 0.8;
+    transform: scale(0.95);
+  }
+}
+
+.sos-btn-text {
+  font-size: 16px;
+  font-weight: 700;
+  color: #fff;
+  letter-spacing: 1px;
+}
+
+.elder-mode .sos-btn {
+  width: 68px;
+  height: 68px;
+  right: 20px;
+  bottom: 130px;
+}
+
+.elder-mode .sos-btn-text {
+  font-size: 20px;
+}