Add optional episode titles to queued and live broadcasts

Store an episode_title on each broadcast, settable from the dashboard
or with set_show.php --title=, and show it under the show name on
index.php and under the heading on live.php.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

sql/schema.sql

@@ -25,6 +25,8 @@ CREATE TABLE IF NOT EXISTS broadcasts (
     created_at   DATETIME NOT NULL DEFAULT CURRENT_TIMESTAMP,
     -- Advertised start time of a queued show; the broadcast still starts when the stream comes online
     scheduled_at DATETIME NULL,
+    -- Optional title for this episode, e.g. "Ethereal and Enya", shown with the show name
+    episode_title VARCHAR(255) NULL,
     started_at   DATETIME NULL,
     last_seen_at DATETIME NULL,
     ended_at     DATETIME NULL,
@@ -37,6 +39,7 @@ CREATE TABLE IF NOT EXISTS broadcasts (
 ALTER TABLE shows ADD COLUMN IF NOT EXISTS description TEXT NULL AFTER name;
 ALTER TABLE shows ADD COLUMN IF NOT EXISTS icon_image VARCHAR(255) NULL AFTER description;
 ALTER TABLE broadcasts ADD COLUMN IF NOT EXISTS scheduled_at DATETIME NULL AFTER created_at;
+ALTER TABLE broadcasts ADD COLUMN IF NOT EXISTS episode_title VARCHAR(255) NULL AFTER scheduled_at;
 
 -- Tracks are cleared ten minutes after their broadcast ends.
 CREATE TABLE IF NOT EXISTS played_tracks (