Fix remaining registerLazySingleton in tutorial markdown files

Changed to registerSingleton for consistency in:
- getting_started.md - Main counter example
- your_first_watch_functions.md - Try It Yourself section
- debugging_tracing.md - Troubleshooting examples (2 instances)

Kept registerLazySingleton in advanced_integration.md as those teach
advanced patterns (scopes, named instances, async init) where lazy
singletons are appropriate.

Author: escamoteur

docs/documentation/watch_it/debugging_tracing.md

@@ -171,7 +171,7 @@ get_it: Object/factory with type TodoManager is not registered inside GetIt
 ```dart
 void main() {
   // Register BEFORE runApp
-  di.registerLazySingleton<TodoManager>(() => TodoManager());
+  di.registerSingleton<TodoManager>(TodoManager());
 
   runApp(MyApp());
 }
@@ -372,7 +372,7 @@ class DebugWidget extends WatchingWidget {
 
 // Test it
 void main() {
-  di.registerLazySingleton<Manager>(() => Manager());
+  di.registerSingleton<Manager>(Manager());
 
   runApp(MaterialApp(
     home: Scaffold(

docs/documentation/watch_it/getting_started.md

@@ -39,7 +39,7 @@ class CounterManager {
 
 // 2. Register it in get_it
 void main() {
-  di.registerLazySingleton<CounterManager>(() => CounterManager());
+  di.registerSingleton<CounterManager>(CounterManager());
   runApp(MyApp());
 }
 

docs/documentation/watch_it/your_first_watch_functions.md

@@ -57,7 +57,7 @@ Add a todo? Widget rebuilds automatically. No `setState`, no `StreamBuilder`.
 
 2. Register it:
    ```dart
-   di.registerLazySingleton<MyManager>(() => MyManager());
+   di.registerSingleton<MyManager>(MyManager());
    ```
 
 3. Watch it: