chore(demo): silence job-control noise on demo shutdown (#41)

disown the stub and server after backgrounding so the cleanup kill does not
print 'Terminated' lines after the demo's closing summary.

Signed-off-by: Val Alexander <bunsthedev@gmail.com>

Author: BunsDev

examples/demo/run-demo.sh

@@ -114,6 +114,8 @@ STUB_PID=$!
 RUST_LOG=info "$ROOT/target/debug/coven-github" serve \
   --config "$DEMO_DIR/config.toml" > "$DEMO_DIR/server.log" 2>&1 &
 SERVER_PID=$!
+# Detach both from job control so shutdown doesn't print 'Terminated' noise.
+disown "$STUB_PID" "$SERVER_PID"
 
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