fix(host): contain capture owners and fail closed

Bound the libpipewire router shutdown without detaching its OS handle, contain GStreamer and pactl children in parent-bound process groups, and make ownership failures terminal through the capture supervisor.\n\nAdd focused lifecycle tests plus a serialized live router teardown gate.

src/host/x11.rs

@@ -10,11 +10,16 @@ use tokio::process::Command;
 use x11rb::connection::Connection;
 use x11rb::protocol::xproto::ConnectionExt;
 
+use super::health;
 use super::pipeline::{self, CaptureHandle};
 use super::quality::EffectiveQuality;
 use crate::cli::HostOpts;
 
-pub async fn start(opts: &HostOpts, quality: &EffectiveQuality) -> Result<CaptureHandle> {
+pub(super) async fn start(
+    opts: &HostOpts,
+    quality: &EffectiveQuality,
+    health: health::Reporter,
+) -> Result<CaptureHandle> {
     let xid = if opts.window {
         Some(pick_window().await?)
     } else {
@@ -60,7 +65,7 @@ pub async fn start(opts: &HostOpts, quality: &EffectiveQuality) -> Result<Captur
     }
 
     // X11 has no leaked fd to clean up, so the post-spawn hook is a no-op.
-    pipeline::spawn(opts, quality, source_dims, source_args, || {}).await
+    pipeline::spawn(opts, quality, source_dims, source_args, health, || {}).await
 }
 
 /// Run `xwininfo` and let the user click the window they want to share, then