Fix AGENTS.md support, changelog viewer, and session model storage

- BREAKING: Renamed AGENT.md to AGENTS.md for project context files
- Added automatic changelog viewer on startup for new sessions
- Added settings manager to track last shown changelog version
- BREAKING: Store provider and modelId separately in session files (fixes #4)
- Fixed markdown list rendering when items contain inline code with cyan formatting
- Added dynamic border component for TUI
- Updated changelog with entries for #4 and #5

packages/coding-agent/src/tui/tui-renderer.ts

@@ -521,7 +521,7 @@ export class TuiRenderer {
 				this.agent.setModel(model);
 
 				// Save model change to session
-				this.sessionManager.saveModelChange(`${model.provider}/${model.id}`);
+				this.sessionManager.saveModelChange(model.provider, model.id);
 
 				// Show confirmation message with proper spacing
 				this.chatContainer.addChild(new Spacer(1));