feat: auto-refresh FileNav on write_file, replace_file_content, and run_command

Backend emits terminal events for write_file, replace_file_content,
and run_command. Frontend showFileNavDir subscriber uses startsWith
path matching to smartly refresh only when the event is relevant:
- write_file/replace_file_content: refresh if path is in current view
- run_command: always refresh (uses root '/' which matches everything)
- Also adds copy-to-clipboard button and code preview full-height fix

src/lib/components/chat/Chat.svelte

@@ -406,11 +406,14 @@
 	};
 
 	const terminalEventHandler = (type: string, data: any) => {
-		if (!data?.path) return;
 		if (type === 'terminal:display_file') {
+			if (!data?.path) return;
 			displayFileHandler(data.path, { showControls, showFileNavPath });
-		} else if (type === 'terminal:write_file') {
+		} else if (type === 'terminal:write_file' || type === 'terminal:replace_file_content') {
+			if (!data?.path) return;
 			showFileNavDir.set(data.path);
+		} else if (type === 'terminal:run_command') {
+			showFileNavDir.set('/');
 		}
 	};