feat: 重构为前后端分离架构并完善设备端演示

- 新增 Web 用户端（登录体系 + 统一 REST API 调用）
- 后端增加用户认证、统一 ApiResponse、CORS 支持
- Android 设备端迁移至 MVVM + DataBinding + Retrofit 网络层
- 完善 README 架构说明与密码学原理文档
- 新增 .gitignore 与持久化数据表说明

web-client/style.css

@@ -0,0 +1,111 @@
+* { box-sizing: border-box; margin: 0; padding: 0; }
+
+body {
+  font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, "PingFang SC",
+    "Hiragino Sans GB", "Microsoft YaHei", sans-serif;
+  background: #f0f4f8;
+  color: #1f2937;
+  min-height: 100vh;
+}
+
+.topbar {
+  display: flex;
+  align-items: center;
+  justify-content: space-between;
+  padding: 16px 32px;
+  background: linear-gradient(135deg, #0f766e, #115e59);
+  color: #fff;
+}
+
+.topbar h1 { font-size: 20px; font-weight: 600; }
+
+.user-info { display: flex; align-items: center; gap: 12px; }
+
+main {
+  max-width: 900px;
+  margin: 24px auto;
+  padding: 0 16px;
+  display: flex;
+  flex-direction: column;
+  gap: 16px;
+}
+
+.panel {
+  background: #fff;
+  border-radius: 12px;
+  padding: 20px 24px;
+  box-shadow: 0 1px 3px rgba(15, 23, 42, .08);
+}
+
+.panel h2 {
+  font-size: 16px;
+  margin-bottom: 12px;
+  color: #0f766e;
+  border-left: 4px solid #0f766e;
+  padding-left: 10px;
+}
+
+.hint { font-size: 13px; color: #6b7280; margin-bottom: 14px; line-height: 1.6; }
+
+.form-row {
+  display: flex;
+  flex-wrap: wrap;
+  gap: 10px;
+  margin-bottom: 12px;
+}
+
+input {
+  flex: 1 1 180px;
+  padding: 10px 12px;
+  border: 1px solid #d1d5db;
+  border-radius: 8px;
+  font-size: 14px;
+  outline: none;
+  transition: border-color .15s;
+}
+
+input:focus { border-color: #0f766e; }
+
+.btn {
+  padding: 10px 18px;
+  border: 1px solid #d1d5db;
+  border-radius: 8px;
+  background: #fff;
+  color: #374151;
+  font-size: 14px;
+  cursor: pointer;
+  transition: all .15s;
+  white-space: nowrap;
+}
+
+.btn:hover { border-color: #0f766e; color: #0f766e; }
+
+.btn-primary { background: #0f766e; border-color: #0f766e; color: #fff; }
+.btn-primary:hover { background: #115e59; color: #fff; }
+
+.btn-sm { padding: 6px 12px; font-size: 13px; }
+
+.result {
+  margin-top: 10px;
+  font-size: 13px;
+  line-height: 1.6;
+  white-space: pre-wrap;
+  word-break: break-all;
+}
+
+.result.ok { color: #047857; }
+.result.err { color: #b91c1c; }
+
+.raw {
+  background: #0f172a;
+  color: #a5f3fc;
+  border-radius: 8px;
+  padding: 14px;
+  font-size: 12px;
+  line-height: 1.6;
+  overflow-x: auto;
+  max-height: 320px;
+  overflow-y: auto;
+}
+
+.hidden { display: none; }