interactive: Host/View entry menu, clipboard copy, player picker

Bare `pixelpass` now opens a dialoguer-driven Host/View menu instead of
going straight to host mode. Host path copies the ticket to the system
clipboard via arboard with silent print-only fallback. View path
prompts for the ticket, then after the local listener binds prompts
mpv-vs-VLC and spawns it detached (setsid + null stdio) so the player
survives pixelpass exiting.

Headless invocations (`pixelpass <ticket>`, `pixelpass --repair`)
unchanged. Per spec at ~/Documents/pixelpass-interactive-mode-spec.md.

src/interactive.rs

@@ -0,0 +1,86 @@
+use anyhow::Result;
+use dialoguer::{Input, Select, theme::ColorfulTheme};
+use iroh_tickets::endpoint::EndpointTicket;
+use std::str::FromStr;
+
+use crate::cli::Cli;
+use crate::{host, viewer};
+
+pub async fn run(cli: Cli) -> Result<()> {
+    print_welcome();
+
+    let theme = ColorfulTheme::default();
+    let choice = Select::with_theme(&theme)
+        .with_prompt("What do you want to do?")
+        .items(&[
+            "Host (share my screen)",
+            "View (watch someone else's screen)",
+        ])
+        .default(0)
+        .interact()?;
+
+    match choice {
+        0 => host::run(cli.into_host_opts(true)).await,
+        _ => {
+            let ticket = prompt_ticket(&theme)?;
+            viewer::run(ticket, cli.into_viewer_opts(true)).await
+        }
+    }
+}
+
+fn print_welcome() {
+    eprintln!();
+    eprintln!("Welcome to PixelPass.");
+    eprintln!();
+}
+
+fn prompt_ticket(theme: &ColorfulTheme) -> Result<EndpointTicket> {
+    loop {
+        let raw: String = Input::with_theme(theme)
+            .with_prompt("Paste the share code you received")
+            .interact_text()?;
+        match EndpointTicket::from_str(raw.trim()) {
+            Ok(t) => return Ok(t),
+            Err(_) => eprintln!("That doesn't look like a share code. Try again."),
+        }
+    }
+}
+
+/// Player options the interactive viewer can launch.
+#[derive(Clone, Copy)]
+pub enum Player {
+    Mpv,
+    Vlc,
+}
+
+impl Player {
+    pub fn spawn(self, url: &str) -> std::io::Result<()> {
+        match self {
+            Player::Mpv => crate::common::process::spawn_detached(
+                "mpv",
+                &[
+                    "--profile=low-latency",
+                    "--untimed",
+                    "--audio-buffer=0.2",
+                    "--demuxer-max-bytes=2M",
+                    "--demuxer-readahead-secs=0.5",
+                    url,
+                ],
+            ),
+            Player::Vlc => crate::common::process::spawn_detached(
+                "vlc",
+                &["--network-caching=200", "--live-caching=200", url],
+            ),
+        }
+    }
+}
+
+pub fn prompt_player() -> Result<Player> {
+    let theme = ColorfulTheme::default();
+    let choice = Select::with_theme(&theme)
+        .with_prompt("Connected. Pick a player to launch")
+        .items(&["mpv", "VLC"])
+        .default(0)
+        .interact()?;
+    Ok(if choice == 0 { Player::Mpv } else { Player::Vlc })
+}