feat: add GET /shows/by-episode/{episode_number} endpoint

Allows looking up shows by episode number instead of internal DB ID,
enabling IRC bot commands like !playlist 530 to resolve directly.

Made-with: Cursor

src/ntr_fetcher/db.py

@@ -239,6 +239,24 @@ class Database:
             for row in rows
         ]
 
+    def get_show_by_episode_number(self, episode_number: int) -> Show | None:
+        conn = self._connect()
+        row = conn.execute(
+            "SELECT id, week_start, week_end, created_at, episode_number "
+            "FROM shows WHERE episode_number = ? LIMIT 1",
+            (episode_number,),
+        ).fetchone()
+        conn.close()
+        if row is None:
+            return None
+        return Show(
+            id=row["id"],
+            week_start=datetime.fromisoformat(row["week_start"]),
+            week_end=datetime.fromisoformat(row["week_end"]),
+            created_at=datetime.fromisoformat(row["created_at"]),
+            episode_number=row["episode_number"],
+        )
+
     def get_latest_episode_number(self) -> int | None:
         conn = self._connect()
         row = conn.execute(