Add reactive UI data binding and observable collections

Introduce observable and computed values, typed widget bindings, validation groups, UI properties, commands, and UI-thread delivery.

Add observable vector and list model support for incrementally updated collections, with filtering and source-row mapping.

Modernize the Flight Booker and CRUD examples and add focused data handling and collection examples demonstrating the new APIs.

Organize the UI binding headers under ui/databinding, expand test coverage for notification and lifetime semantics, and document API selection, validation, ownership, threading, and performance behavior.

.ecode/project_build.json

@@ -399,6 +399,18 @@
         "command": "${project_root}/bin/eepp-sprites-debug",
         "name": "eepp-sprites-debug",
         "working_dir": "${project_root}/bin"
+      },
+      {
+        "args": "",
+        "command": "${project_root}/bin/eepp-ui-data-collections-debug",
+        "name": "eepp-ui-data-collections-debug",
+        "working_dir": "${project_root}/bin"
+      },
+      {
+        "args": "",
+        "command": "${project_root}/bin/eepp-ui-data-handling-debug",
+        "name": "eepp-ui-data-handling-debug",
+        "working_dir": "${project_root}/bin"
       }
     ],
     "var": {