feat: add McpScreen phase 2 display tools

Apps/McpScreen/IMPLEMENTATION_PLAN.md

@@ -64,9 +64,12 @@ Pending verification:
 
 Tactility unloads external-app ELF memory immediately after `onDestroy`
 returns. An app task blocked in `accept()` therefore cannot be allowed to
-survive destruction. The HTTP listener is non-blocking, client reads have
-short timeouts, and `onDestroy` closes sockets, waits for the worker to signal
-exit, then deletes the suspended worker task before returning.
+survive destruction. The HTTP listener is non-blocking and client reads have
+short timeouts. `onHide` only clears the run flag and returns immediately so
+it does not block Tactility's GUI lifecycle or close an lwIP descriptor from
+the wrong task. The worker owns the socket shutdown, then suspends itself
+asynchronously. The next `onShow` reaps it before starting a new worker, while
+`onDestroy` waits for and deletes it before returning.
 
 ## Design principles
 
@@ -124,20 +127,20 @@ implementation is easier to validate.
 
 - `onCreate`
   - Allocate application state.
-  - Start UDP discovery and HTTP MCP service tasks.
 - `onShow`
   - Build the dashboard and MCP-controlled display canvas.
   - Attach the current UI objects to the shared application state.
+  - Start the HTTP MCP service.
 - `onHide`
+  - Signal the HTTP MCP service to stop without blocking the GUI lifecycle.
   - Detach and invalidate UI object pointers.
-  - Keep network services running while the application is merely hidden, if
-    Tactility preserves the app instance.
 - `onDestroy`
-  - Stop tasks and sockets.
+  - Join/delete any remaining worker and close sockets as a safety fallback.
   - Release buffers, devices, and application state.
 
-The first implementation slice must explicitly verify whether Tactility keeps
-the app process and `onCreate` state alive while another app is visible.
+The MCP server is deliberately foreground-only. Tactility does not need to
+keep the listener or display-control task active while another app owns the
+screen.
 
 ### FreeRTOS responsibilities