fix: flush stdout prompts in first-run config wizard

The prompt_config() function used print!() without flushing stdout,
causing all prompts to be buffered and invisible to the user. The
program appeared to hang silently after 'No config found — first-time
setup'.

Changes:
- Add std::io::stdout().flush().unwrap() after each print!() prompt
- Style prompts with cyan '→' prefix to match CLI conventions
- Show default values in square brackets for relay URL and label
- Use hostname() as default label (was previously Optional/None)
- Add blank line after prompts before '✓ Config saved'

crates/client/src/main.rs

@@ -90,31 +90,42 @@ impl Config {
 }
 
 fn prompt_config() -> Config {
+    use std::io::Write;
+
     let relay_url = {
-        print!("  Relay server URL [default: wss://remote.agent-helios.me/ws]: ");
+        let default = "wss://remote.agent-helios.me/ws";
+        print!("  {} Relay URL [{}]: ", "→".cyan().bold(), default);
+        std::io::stdout().flush().unwrap();
         let mut input = String::new();
         std::io::stdin().read_line(&mut input).unwrap();
         let trimmed = input.trim();
         if trimmed.is_empty() {
-            "wss://remote.agent-helios.me/ws".to_string()
+            default.to_string()
         } else {
             trimmed.to_string()
         }
     };
 
     let api_key = {
-        print!("  API Key: ");
+        print!("  {} API Key: ", "→".cyan().bold());
+        std::io::stdout().flush().unwrap();
         let mut input = String::new();
         std::io::stdin().read_line(&mut input).unwrap();
         input.trim().to_string()
     };
 
     let label = {
-        print!("  Label for this machine (optional, press Enter to skip): ");
+        let default_label = hostname();
+        print!("  {} Label for this PC [{}]: ", "→".cyan().bold(), default_label);
+        std::io::stdout().flush().unwrap();
         let mut input = String::new();
         std::io::stdin().read_line(&mut input).unwrap();
         let trimmed = input.trim().to_string();
-        if trimmed.is_empty() { None } else { Some(trimmed) }
+        if trimmed.is_empty() {
+            Some(default_label)
+        } else {
+            Some(trimmed)
+        }
     };
 
     Config { relay_url, api_key, label }
@@ -136,6 +147,7 @@ async fn main() {
             log_status!("No config found — first-time setup");
             println!();
             let c = prompt_config();
+            println!();
             if let Err(e) = c.save() {
                 log_err!("Failed to save config: {e}");
             } else {