feat(i18n): convert LevelMeter to t() (Batch F)

src/lib/components/LevelMeter.svelte

@@ -3,6 +3,7 @@
   // system/loopback level (green) and — when the mic is enabled — the microphone
   // level overlaid in the accent colour, so both sides of the call are visible
   // at a glance. Each stream shows an rms fill + a peak marker.
+  import { t } from "../i18n/index.svelte";
   let {
     rms,
     peak,
@@ -29,7 +30,7 @@
 <div
   class="meter"
   role="meter"
-  aria-label={showMic ? "System and microphone input level" : "System input level"}
+  aria-label={showMic ? t("levelmeter.system_mic") : t("levelmeter.system")}
   aria-valuenow={Math.round(Math.max(rmsPct, showMic ? micRmsPct : 0))}
   aria-valuemin={0}
   aria-valuemax={100}