app-module events & callstack config, crash diagnostics (#630)

- Apps can specify task stack depth and preferred memory placement in their manifests.
- App identifiers are validated against length and character requirements.
- Crash diagnostics now show the crash cause, reason, fault address, call stack, and program-counter details, with logs saved for review.
- App closing is more consistent across built-in screens. There's now a dedicated function, and the old _emit() function is made private.
- Crash diagnostics no longer display a QR code without a call stack.
- Improved memory allocation for unrestricted requests.

Modules/app-module/include/app/metadata.h

@@ -50,6 +50,12 @@ struct AppMetadata {
      * Must be NULL-terminated.
      */
     char requires_device_id[APP_METADATA_REQUIRES_DEVICE_ID_LENGTH + 1];
+
+    /**
+     * Stack depth (in words) for the app's task. Optional; 0 means scheduler default.
+     * @warning Avoid default values: the default is conservative, which wastes memory.
+     */
+    uint32_t stack_depth;
 };
 
 /**