refactor: restructure entire project for human maintainability

Server:
- Add Express framework, replace custom router/request parser
- Create DAO layer (12 files) centralizing all 73 SQL queries
- Rewrite 7 route files as thin Express controllers calling DAOs
- Add SCF-to-Express adapter (lib/serverless.js)
- Add auth middleware (middleware/auth.js)
- Remove dead code from lib/auth.js

Admin console:
- Extract DataTable component (table + pagination)
- Extract ConfirmModal component (modal + form styles)
- Create listMixin for paginated list pages
- Move form styles to common.css for slot compatibility
- Refactor device + subscription pages as examples

Miniprogram:
- Split 734-line BLE monolith into 4 focused modules
  (protocol, connection, commands, barrel index)
- Create API module (utils/api.js) with named functions
- Create page utilities (utils/page.js)
- Refactor index + profile pages to use API module

miniprogram/utils/page.js

@@ -0,0 +1,25 @@
+var app = getApp()
+
+/** Get status bar height for custom navigation pages */
+function getStatusBarHeight() {
+  return app.globalData.statusBarHeight || 44
+}
+
+/** Standard back navigation with fallback */
+function navigateBack(fallbackUrl) {
+  wx.navigateBack({
+    fail: function () {
+      if (fallbackUrl) {
+        wx.reLaunch({ url: fallbackUrl })
+      }
+    }
+  })
+}
+
+/** Check if dev mode is enabled */
+function isDevMode() {
+  var config = require('../config/env')
+  return config.__DEV__ || false
+}
+
+module.exports = { getStatusBarHeight: getStatusBarHeight, navigateBack: navigateBack, isDevMode: isDevMode }