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/cli.rs

@@ -13,6 +13,12 @@ pub struct Cli {
     pub ticket: Option<String>,
 
     // ── host options ──────────────────────────────────────────────────
+    /// Run as host without the interactive menu. Equivalent to picking
+    /// "Host" in the menu, but headless — for scripting and the --gui
+    /// front-end, which drives this binary as a child process.
+    #[arg(long)]
+    pub host: bool,
+
     /// Pick a single window instead of the whole screen.
     #[arg(long)]
     pub window: bool,