feat(settings): Audio Devices section under Hardware

A <select> defaulting to "Default system audio", populated from the
enumerated render devices — picking one overrides which device
WhispAssist loopback-captures from instead of always following
Windows' system default.

src/lib/views/Settings.svelte

@@ -563,6 +563,25 @@
             to load.
           </p>
 
+          <h4>Audio Devices</h4>
+          <label
+            >Recording device
+            <select
+              value={settings.settings.audio_output_device ?? ""}
+              onchange={(e) =>
+                settings.setAudioOutputDevice((e.target as HTMLSelectElement).value || null)}
+            >
+              <option value="">Default system audio</option>
+              {#each settings.audioDevices as d (d.id)}
+                <option value={d.id}>{d.name}</option>
+              {/each}
+            </select>
+          </label>
+          <p class="muted">
+            WhispAssist records whatever this device plays (loopback) — not a microphone. Pick a
+            specific output if you don't want it following Windows' system default.
+          </p>
+
           {#if settings.hardware.npu?.present}
             {@const npu = settings.hardware.npu}
             {@const ready = npu.runtimeReady && npu.modelInstalled}