refine: dashboard review fixes - echo removal, model escape, RMS gate, fd leak, mic cleanup

Reviewer feedback: remove AudioContext destination echo, escape model names, add RMS gate to skip silence, close mkstemp fd, clean up mic on WS close. Tests updated for the RMS gate.

tests/integration/test_api.py

@@ -147,7 +147,9 @@ class TestJobs:
         # 조회
         r = client.get(f"/v1/jobs/{job_id}", headers=headers)
         assert r.status_code == 200
-        assert r.json()["status"] == "queued"
+        body = r.json()
+        assert body["status"] == "queued"
+        assert body["source_name"] == "meeting.mp3"  # 대시보드 파일 컬럼용
 
         # 결과는 아직 없음
         r = client.get(f"/v1/jobs/{job_id}/result", headers=headers)