fix(windows): prevent console window flash

- Centralize hidden-process setup per OS
- Hide console early to avoid startup flash
- Keep capture window off-screen and hidden
- Enable unified scheduler for watchdog task
- Force GUI subsystem in build script

lib/helpers/hide_stub.go

@@ -0,0 +1,9 @@
+//go:build !windows
+
+package helpers
+
+import "syscall"
+
+func HiddenSysProcAttr() *syscall.SysProcAttr { return nil }
+
+func HiddenDetachedSysProcAttr() *syscall.SysProcAttr { return nil }