GitHub Copilot: auto-enable models, fix gpt-5 API, normalize tool call IDs

- Auto-enable all models after /login via POST /models/{model}/policy
- Use openai-responses API for gpt-5/o3/o4 models (not accessible via completions)
- Normalize tool call IDs when switching between github-copilot models with different APIs
  (fixes #198: openai-responses generates 450+ char IDs with special chars that break other models)
- Update README with streamlined GitHub Copilot docs

packages/coding-agent/src/modes/interactive/interactive-mode.ts

@@ -1419,6 +1419,10 @@ export class InteractiveMode {
 										this.ui.requestRender();
 									});
 								},
+								(message) => {
+									this.chatContainer.addChild(new Text(theme.fg("dim", message), 1, 0));
+									this.ui.requestRender();
+								},
 							);
 
 							invalidateOAuthCache();