fix: use ASCII prompt to prevent backspace corruption

rust/.claude/sessions/session-1775007981374.json

@@ -0,0 +1 @@
+{"messages":[],"version":1}

rust/.claude/sessions/session-1775008007069.json

@@ -0,0 +1 @@
+{"messages":[],"version":1}

rust/crates/rusty-claude-cli/src/main.rs

@@ -878,7 +878,7 @@ fn run_repl(
     permission_mode: PermissionMode,
 ) -> Result<(), Box<dyn std::error::Error>> {
     let mut cli = LiveCli::new(model, true, allowed_tools, permission_mode)?;
-    let mut editor = input::LineEditor::new("🦞 ", slash_command_completion_candidates());
+    let mut editor = input::LineEditor::new("> ", slash_command_completion_candidates());
     println!("{}", cli.startup_banner());
 
     loop {