fix: waiter Ctrl+C not responding in interactive mode

rawmode_linux.go only cleared ICANON|ECHO but left ISIG enabled,
so the terminal driver caught Ctrl+C and generated SIGINT.
signal.Notify caught the SIGINT but no goroutine consumed the
channel, effectively swallowing the signal.

Fix: also clear ISIG so Ctrl+C is delivered as byte 0x03,
which the line editor handles with os.Exit(130). Also set
VMIN=1, VTIME=0 for proper blocking read behavior.

cmd/waiter/rawmode_defs.go

@@ -15,4 +15,7 @@ const (
 	TCSETS = 0x5402
 	ICANON = 0x2
 	ECHO   = 0x8
+	ISIG   = 0x1
+	VMIN   = 6
+	VTIME  = 5
 )