feat(command-line): adjustable command line opacity

COMMANDLINEOPACITY (20-100 percent, default 100) and a slider under
Options > Display make the floating command line's panels see-through,
so the drawing stays visible behind it. The input field stays opaque
for legibility. The value is an application setting that persists.

Refs #1494

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

locales/lo-LA/opencadstudio.ftl

@@ -281,6 +281,7 @@ command-copy =
     .mode = COPY  ປ້ອນຕົວເລືອກໂໝດການຄັດລອກ [Single/Multiple] <Multiple>:
 
 common =
+    .command-line-opacity = ຄວາມທຶບຂອງແຖວຄຳສັ່ງ
     .txtexp-no-text-selected = TXTEXP: ບໍ່ໄດ້ເລືອກຂໍ້ຄວາມ.
     .angle-override-shown = ກຳນົດມຸມແທນ: __ocs_fmt_0__
     .remote-image-url-could-not-be-fetched-the-request-timed-out = ບໍ່ສາມາດດຶງຮູບພາບທາງໄກ "__ocs_fmt_0__" ໄດ້: ການຮ້ອງຂໍໝົດເວລາ.