refactor(coding-agent): restructured loading animation lifecycle into ensureLoadingAnimation

- Extracted loading animation lifecycle management into centralized ensureLoadingAnimation() method.
- Consolidated duplicate loading animation setup across event-controller and interactive-mode into single reusable method.
- Updated showError() to properly clean up loading animation state when errors occur.
- Added comprehensive test coverage for InputController escape key behavior with optimistic submission.

packages/coding-agent/src/modes/controllers/input-controller.ts

@@ -339,6 +339,7 @@ export class InputController {
 				};
 				this.ctx.addMessageToChat(optimisticMessage);
 				this.ctx.editor.setText("");
+				this.ctx.ensureLoadingAnimation();
 				this.ctx.ui.requestRender();
 
 				this.ctx.onInputCallback({ text, images });