screenshare: log the pixelpass-host and player argv on spawn

The screen-share code only logged pixelpass's high-level JSON events, never
the argv it spawned children with, so a field log couldn't confirm which
encode/viewer settings actually reached the helpers — e.g. the per-call
quality's --bitrate (host) or the hardware-decode --avcodec-hw/--hwdec flag
(player). Log both verbatim at spawn: host args carry no secret, and the
player line omits the local stream URL. Logged per attempt so a player
fallback is visible too.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/screenshare/mod.rs

@@ -370,8 +370,13 @@ pub async fn spawn_host(
     quality: ShareQuality,
     notices: Option<tokio::sync::mpsc::UnboundedSender<PixelpassEvent>>,
 ) -> std::io::Result<(Child, String)> {
+    let args = host_args(audio_app, settings, quality);
+    // Log the exact argv we hand pixelpass so a field log can confirm which
+    // encode/quality flags (e.g. --bitrate) actually reached the host — these
+    // are local flags with no ticket/secret, so logging them verbatim is safe.
+    crate::log_msg(&format!("pixelpass host spawn: {} {}", bin.display(), args.join(" ")));
     let mut child = Command::new(bin)
-        .args(host_args(audio_app, settings, quality))
+        .args(&args)
         .stdin(Stdio::null())
         .stdout(Stdio::piped())
         // Capture stderr (not null): pixelpass prints its startup precondition
@@ -686,6 +691,12 @@ fn vlc_args(settings: &ScreenShareSettings) -> Vec<String> {
 }
 
 fn spawn_player(bin: &str, args: &[String], url: &str) -> std::io::Result<Child> {
+    // Log the player + its flags (mpv/vlc, incl. hardware-decode: --hwdec /
+    // --avcodec-hw) so a field log can confirm the viewer settings reached the
+    // player. The `url` is omitted deliberately — it is the local stream address
+    // and is not needed to verify the flags. Logged on each attempt, so a
+    // fallback from the preferred player to the other one is visible too.
+    crate::log_msg(&format!("player spawn: {bin} {}", args.join(" ")));
     Command::new(bin)
         .args(args)
         .arg(url)