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

tests/test_db.py

@@ -272,6 +272,20 @@ def test_update_show_episode_number(db):
     assert show2.episode_number == 521
 
 
+def test_get_show_by_episode_number(db):
+    week_start = datetime(2026, 1, 8, 3, 0, 0, tzinfo=timezone.utc)
+    week_end = datetime(2026, 1, 15, 3, 0, 0, tzinfo=timezone.utc)
+    show = db.get_or_create_show(week_start, week_end, episode_number=521)
+    result = db.get_show_by_episode_number(521)
+    assert result is not None
+    assert result.id == show.id
+    assert result.episode_number == 521
+
+
+def test_get_show_by_episode_number_missing(db):
+    assert db.get_show_by_episode_number(999) is None
+
+
 def test_has_track_in_show(db):
     week_start = datetime(2026, 3, 13, 2, 0, 0, tzinfo=timezone.utc)
     week_end = datetime(2026, 3, 20, 2, 0, 0, tzinfo=timezone.utc)