feat(cli): --host flag for headless hosting

Hosting was only reachable through the interactive dialoguer menu; there
was no way to start a host non-interactively. Add a --host flag that runs
host::run directly (interactive=false), bypassing the menu. Useful for
scripting and required by the upcoming --gui front-end, which drives this
binary as a child process. Guards against --host + ticket (contradictory).

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

src/main.rs

@@ -28,6 +28,16 @@ async fn main() -> Result<()> {
         return interactive::run_reconfigure().await;
     }
 
+    if cli.host {
+        if cli.ticket.is_some() {
+            anyhow::bail!(
+                "--host and a ticket argument are mutually exclusive: --host shares your \
+                 screen, a ticket views someone else's."
+            );
+        }
+        return host::run(cli.into_host_opts(false)).await;
+    }
+
     match cli.ticket.as_deref() {
         Some(s) => {
             let ticket: EndpointTicket = s.parse().map_err(|e| {