windows: no console window for the release app and its children

- the oak-editor release build lacked the
  `windows_subsystem = "windows"` crate attribute, so launching the
  installed app opened a console window next to the editor (debug builds
  keep the console so `cargo run` shows logs);
- oak-worker, the OFX host and the ffmpeg/ffprobe helpers are
  console-subsystem binaries spawned by the GUI app, so each spawn now
  carries CREATE_NO_WINDOW through the shared
  oak_core::miscutils::hide_console_window helper (a no-op off Windows).

crates/oak-render/src/ofxhost.rs

@@ -466,6 +466,8 @@ impl OfxHost {
 		for (key, value) in &config.env {
 			command.env(key, value);
 		}
+		// A GUI Oak spawning a console child would flash a console window.
+		oak_core::miscutils::hide_console_window(&mut command);
 		let mut child = command
 			.spawn()
 			.map_err(|e| Error::Failed(format!("spawn OFX host {}: {e}", bin.display())))?;

crates/oak-render/src/procpool.rs

@@ -1950,14 +1950,18 @@ impl ProcessDispatcher {
 		);
 		let shm = ShmRegionView::create(&key, inner.slots, inner.slot_bytes)?;
 
-		let mut child = Command::new(&inner.bin)
+		let mut command = Command::new(&inner.bin);
+		command
 			// Auto backend: prefer the GPU, fall back to the CPU renderer
 			// (M16 S1 — the worker tolerates a GPU init failure and keeps
 			// evaluating headless).
 			.args(["--backend", "auto"])
 			.stdin(Stdio::piped())
 			.stdout(Stdio::piped())
-			.stderr(Stdio::inherit())
+			.stderr(Stdio::inherit());
+		// A GUI Oak spawning a console child would flash a console window.
+		oak_core::miscutils::hide_console_window(&mut command);
+		let mut child = command
 			.spawn()
 			.map_err(|e| Error::Failed(format!("spawn oak-worker: {e}")))?;
 		let stdin = child.stdin.take();