Add login flow, session routing, and MainTab shell aligned with reference UI.

Implement token-based root routing, Android-matched login screen, five-slot MainTabBar with scan action, and placeholder tab pages.

Co-authored-by: Cursor <cursoragent@cursor.com>

suixinkan/Assets.xcassets/icon_cb_privacy_selected.imageset/Contents.json

@@ -0,0 +1,12 @@
+{
+  "images" : [
+    {
+      "filename" : "icon_cb_privacy_selected.png",
+      "idiom" : "universal"
+    }
+  ],
+  "info" : {
+    "author" : "xcode",
+    "version" : 1
+  }
+}