fix: Filter out Stereo Mix and select real microphone device

- Filter out "立體聲混音" (Stereo Mix) devices which are not real microphones
- Skip the "default" device which may point to Stereo Mix
- Prefer "communications" device or devices with "麥克風/microphone" in label
- Use exact deviceId constraint for better device selection
- Add fallback to preferred constraint if exact fails
- Add more detailed console logging for debugging

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

.gitignore

@@ -56,3 +56,4 @@ backend/record/
 openspec/
 AGENTS.md
 CLAUDE.md
+.running_pids

client/src/pages/meeting-detail.html

@@ -415,14 +415,39 @@
           return;
         }
 
-        // Try with simple constraints first, fall back to more specific ones
+        // Filter out Stereo Mix (立體聲混音) - it's not a real microphone
+        const realMicrophones = audioInputs.filter(d =>
+          !d.label.includes('立體聲混音') &&
+          !d.label.toLowerCase().includes('stereo mix') &&
+          d.deviceId !== 'default'  // Skip default which might be Stereo Mix
+        );
+
+        // Prefer communications device or actual microphone
+        let selectedMic = realMicrophones.find(d =>
+          d.deviceId === 'communications' ||
+          d.label.includes('麥克風') ||
+          d.label.toLowerCase().includes('microphone')
+        ) || realMicrophones[0];
+
+        console.log('Real microphones found:', realMicrophones.length);
+        console.log('Selected microphone:', selectedMic);
+
+        if (!selectedMic) {
+          alert('No real microphone found. Only Stereo Mix detected. Please connect a microphone.');
+          return;
+        }
+
+        // Try with the selected microphone
         try {
-          mediaStream = await navigator.mediaDevices.getUserMedia({ audio: true });
-        } catch (simpleErr) {
-          console.warn('Simple audio constraints failed, trying with device ID:', simpleErr);
-          // Try with explicit device ID
           mediaStream = await navigator.mediaDevices.getUserMedia({
-            audio: { deviceId: audioInputs[0].deviceId }
+            audio: { deviceId: { exact: selectedMic.deviceId } }
+          });
+          console.log('Successfully connected to:', selectedMic.label);
+        } catch (exactErr) {
+          console.warn('Exact device ID failed, trying preferred:', exactErr);
+          // Fallback: try with preferred instead of exact
+          mediaStream = await navigator.mediaDevices.getUserMedia({
+            audio: { deviceId: selectedMic.deviceId }
           });
         }