fix(music-lab): revenue avg_rpm 공식 수정 + UNIQUE 제약 + 테스트 보강

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

music-lab/app/db.py

@@ -131,7 +131,8 @@ def init_db() -> None:
                 rpm_usd          REAL    NOT NULL DEFAULT 0.0,
                 country          TEXT NOT NULL DEFAULT '',
                 source           TEXT NOT NULL DEFAULT 'manual',
-                created_at       TEXT NOT NULL DEFAULT (strftime('%Y-%m-%dT%H:%M:%fZ','now'))
+                created_at       TEXT NOT NULL DEFAULT (strftime('%Y-%m-%dT%H:%M:%fZ','now')),
+                UNIQUE(yt_video_id, record_month, country)
             )
         """)
         conn.execute("CREATE INDEX IF NOT EXISTS idx_rr_month ON revenue_records(record_month DESC)")
@@ -567,7 +568,7 @@ def get_revenue_dashboard() -> dict:
         ).fetchone()
         by_month = conn.execute(
             """SELECT record_month, SUM(revenue_usd) as revenue, SUM(views) as views,
-               AVG(rpm_usd) as avg_rpm FROM revenue_records
+               CASE WHEN SUM(views) > 0 THEN ROUND(SUM(revenue_usd) / SUM(views) * 1000, 4) ELSE 0.0 END as avg_rpm FROM revenue_records
                GROUP BY record_month ORDER BY record_month DESC LIMIT 12"""
         ).fetchall()
         by_country = conn.execute(