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/cli.rs

@@ -5,8 +5,8 @@ use clap::{Parser, ValueEnum};
     name = "pixelpass",
     version,
     about = "P2P screen sharing over iroh + ffmpeg",
-    long_about = "Run with no arguments to host (prints a ticket to share). \
-                  Pass a ticket to view."
+    long_about = "Run with no arguments for an interactive Host/View menu. \
+                  Pass a ticket positionally to skip the menu and view headlessly."
 )]
 pub struct Cli {
     /// iroh ticket. If present, runs as viewer. If absent, runs as host.
@@ -76,15 +76,17 @@ pub struct HostOpts {
     pub framerate: u32,
     pub no_hwencode: bool,
     pub low_latency: bool,
+    pub interactive: bool,
 }
 
 #[derive(Debug, Clone)]
 pub struct ViewerOpts {
     pub port: u16,
+    pub interactive: bool,
 }
 
 impl Cli {
-    pub fn into_host_opts(self) -> HostOpts {
+    pub fn into_host_opts(self, interactive: bool) -> HostOpts {
         HostOpts {
             window: self.window,
             app: self.app,
@@ -94,10 +96,11 @@ impl Cli {
             framerate: self.framerate,
             no_hwencode: self.no_hwencode,
             low_latency: self.low_latency,
+            interactive,
         }
     }
 
-    pub fn into_viewer_opts(self) -> ViewerOpts {
-        ViewerOpts { port: self.port }
+    pub fn into_viewer_opts(self, interactive: bool) -> ViewerOpts {
+        ViewerOpts { port: self.port, interactive }
     }
 }