chore: add release notes

Author: jonas-meyer

release-content/release-notes/observer_run_conditions.md

@@ -0,0 +1,26 @@
+---
+title: Observer Run Conditions
+authors: ["@jonas-meyer"]
+pull_requests: [22602]
+---
+
+Observers can now use run conditions with `.run_if()`, the same pattern systems use for conditional execution.
+
+```rust
+#[derive(Resource)]
+struct GamePaused(bool);
+
+// Observer only runs when game is not paused
+app.add_observer(
+    on_damage.run_if(|paused: Res<GamePaused>| !paused.0)
+);
+
+// Multiple conditions can be chained (AND semantics)
+app.add_observer(
+    on_damage
+        .run_if(|paused: Res<GamePaused>| !paused.0)
+        .run_if(resource_exists::<Player>)
+);
+```
+
+This works with `add_observer`, entity `.observe()`, and the `Observer` builder pattern.