fix(tui): preserved TUI initial scrollback unless clear was requested

- Updated the initial render intent to carry a `clearScrollback` flag.
- Adjusted first-frame rendering logic to preserve existing scrollback by default and clear only when requested.
- Added `resolver` stubs to coding-agent and web-search test registries for interface compatibility.

packages/coding-agent/test/memories-runtime.test.ts

@@ -46,6 +46,7 @@ function createModelRegistry(model: Model): any {
 		find: vi.fn(() => model),
 		getAll: vi.fn(() => [model]),
 		getApiKey: vi.fn(async () => "test-api-key"),
+		resolver: vi.fn(() => async () => "test-api-key"),
 	};
 }