Add recently played tracking with shows and broadcasts

- sql/schema.sql: shows, broadcasts and played_tracks tables, seeded
  with the five shows
- cli/poll_icecast.php: cron-run poller that records broadcasts and
  tracks every 15 seconds while streaming; tracks are cleared ten
  minutes after a broadcast ends
- cli/set_show.php: queue the next show, or assign one to the live
  broadcast
- recently_played.php: track history rows for live.php, with album art
  and album title linking to Last.fm
- live.php: recently played list, show name in heading, and per-show
  header background
- includes/icecast.php: Icecast parsing, album art and Last.fm helpers
  shared by now_playing.php and the poller
- includes/db.php: use UTC for the database session

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

sql/schema.sql

@@ -0,0 +1,48 @@
+-- Radio Free Elsewhere database schema.
+-- Apply with: mysql -u <user> -p <database> < sql/schema.sql
+-- All DATETIME values are stored in UTC (includes/db.php sets the session time zone).
+
+CREATE TABLE IF NOT EXISTS shows (
+    id               INT UNSIGNED AUTO_INCREMENT PRIMARY KEY,
+    slug             VARCHAR(64)  NOT NULL UNIQUE,
+    name             VARCHAR(255) NOT NULL,
+    -- Filename in images/backgrounds/ used as the live.php header background; NULL keeps the default
+    background_image VARCHAR(255) NULL,
+    created_at       DATETIME     NOT NULL DEFAULT CURRENT_TIMESTAMP
+) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_unicode_ci;
+
+-- One row per streaming session.
+-- Pending (queued by cli/set_show.php): started_at IS NULL
+-- Live:                                 started_at set, ended_at IS NULL
+-- Ended:                                ended_at set
+CREATE TABLE IF NOT EXISTS broadcasts (
+    id           INT UNSIGNED AUTO_INCREMENT PRIMARY KEY,
+    show_id      INT UNSIGNED NULL,
+    created_at   DATETIME NOT NULL DEFAULT CURRENT_TIMESTAMP,
+    started_at   DATETIME NULL,
+    last_seen_at DATETIME NULL,
+    ended_at     DATETIME NULL,
+    INDEX (started_at),
+    INDEX (ended_at),
+    FOREIGN KEY (show_id) REFERENCES shows (id) ON DELETE SET NULL
+) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_unicode_ci;
+
+-- Tracks are cleared ten minutes after their broadcast ends.
+CREATE TABLE IF NOT EXISTS played_tracks (
+    id           INT UNSIGNED AUTO_INCREMENT PRIMARY KEY,
+    broadcast_id INT UNSIGNED NOT NULL,
+    played_at    DATETIME     NOT NULL DEFAULT CURRENT_TIMESTAMP,
+    title        VARCHAR(255) NOT NULL,
+    artist       VARCHAR(255) NOT NULL DEFAULT '',
+    album        VARCHAR(255) NOT NULL DEFAULT '',
+    art_url      VARCHAR(512) NOT NULL DEFAULT '',
+    INDEX (broadcast_id, played_at),
+    FOREIGN KEY (broadcast_id) REFERENCES broadcasts (id) ON DELETE CASCADE
+) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_unicode_ci;
+
+INSERT IGNORE INTO shows (slug, name) VALUES
+    ('omorains-pub',      'O''Morain''s Pub'),
+    ('cosmoeuphoria',     'Cosmoeuphoria'),
+    ('bisexual-surfers',  'Bisexual Surfers From the Twilight of Time'),
+    ('the-bollocks',      'The Bollocks'),
+    ('the-spin',          'The Spin');