Windows: ffmpeg/ffprobe subprocesses flash console windows (CREATE_NO_WINDOW missing in process_tree::configure_command)

[owenglenfehr]

Summary

On Windows, every ffmpeg/ffprobe subprocess flashes a console window.
Starting playback on a timeline spawns roughly ten of them, producing
visible flicker and focus churn for several seconds before the first frame.

Cause

opentake-process-tree::configure_command is the single choke point for
Windows spawn flags (crates/opentake-process-tree/src/lib.rs:40). It sets:

CREATE_NEW_PROCESS_GROUP | CREATE_SUSPENDED

but not CREATE_NO_WINDOW, so every child process gets a console window.

opentake-media/src/ff.rs routes its spawns through that helper
(crate::process_tree::configure_command(command.as_std_mut()) at lines
241 and 313), so one added flag should cover the ffmpeg/ffprobe paths.

Suggested fix

use windows_sys::Win32::System::Threading::{
    CREATE_NEW_PROCESS_GROUP, CREATE_NO_WINDOW, CREATE_SUSPENDED,
};
command.creation_flags(
    CREATE_NEW_PROCESS_GROUP | CREATE_SUSPENDED | CREATE_NO_WINDOW,
);

CREATE_NO_WINDOW composes fine with the existing two flags and does not
affect the suspend-then-assign-to-Job-Object sequence the doc comment
describes.

Also worth checking ff.rs:726 (FfmpegCommand::new_with_path) and
ff.rs:733 (Command::new(ffmpeg_path())), which do not appear to call
configure_command and may need the flag separately.

Environment

v1.0.0-beta.5, official Windows release build, Windows 11.

Impact

Cosmetic but constant — visible on every playback start, scrub and probe,
and it steals focus. Note this is separate from the spawn count itself:
suppressing the windows makes playback quiet, not faster.