Add show management and going-live controls to admin

- admin/shows.php: list shows
- admin/show_edit.php: add, edit and delete shows, with validated
  background image uploads saved under generated names
- admin/index.php: queue the next show, switch the live show, or clear
  the queue
- includes/broadcasts.php: setBroadcastShow() and clearQueuedShow(),
  shared by the dashboard and cli/set_show.php
- includes/admin_layout.php: flash messages and Shows nav link

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

admin/index.php

@@ -6,22 +6,75 @@ require __DIR__ . '/../includes/broadcasts.php';
 $admin = requireAdmin();
 $db = getDB();
 
+if ($_SERVER['REQUEST_METHOD'] === 'POST') {
+    verifyCsrf();
+    $action = $_POST['action'] ?? '';
+
+    if ($action === 'set_show') {
+        $stmt = $db->prepare('SELECT id, name FROM shows WHERE id = ?');
+        $stmt->execute([(int)($_POST['show_id'] ?? 0)]);
+        $show = $stmt->fetch();
+        if (!$show) {
+            flash('Please choose a show.', 'error');
+        } elseif (setBroadcastShow($db, (int)$show['id']) === 'live') {
+            flash("The live broadcast is now {$show['name']}.");
+        } else {
+            flash("{$show['name']} is queued. It will go live as soon as the stream starts.");
+        }
+    } elseif ($action === 'clear_queue') {
+        clearQueuedShow($db);
+        flash('The queued show has been cleared.');
+    }
+
+    header('Location: index.php');
+    exit;
+}
+
 $live = liveBroadcast($db);
-$show = currentShow($db);
+$current = currentShow($db);
+$shows = $db->query('SELECT id, name FROM shows ORDER BY name')->fetchAll();
 
 adminHeader('Dashboard', $admin);
 ?>
-				<p>Logged in as <strong><?= e($admin['username']) ?></strong>.</p>
-
 				<h3>Broadcast status</h3>
 				<p>
 <?php if ($live): ?>
-					Live now<?= $show ? ': <strong>' . e($show['name']) . '</strong>' : ' (no show set)' ?>, since <?= e($live['started_at']) ?> UTC.
-<?php elseif ($show): ?>
-					Offline. <strong><?= e($show['name']) ?></strong> is queued for the next broadcast.
+					<strong>Live now</strong><?= $current ? ': ' . e($current['name']) : ' (no show set)' ?>, since <?= e($live['started_at']) ?> UTC.
+<?php elseif ($current): ?>
+					Offline. <strong><?= e($current['name']) ?></strong> is queued for the next broadcast.
 <?php else: ?>
 					Offline. No show is queued.
 <?php endif; ?>
 				</p>
+
+				<h3><?= $live ? 'Change the live show' : 'Queue the next show' ?></h3>
+				<p><?= $live
+				    ? 'Switch which show the live page and recently played list belong to.'
+				    : 'Choose the show before you start streaming. The broadcast goes live on the site automatically when the stream comes online.' ?></p>
+				<form method="post" action="index.php">
+					<?= csrfField() ?>
+					<input type="hidden" name="action" value="set_show" />
+					<div class="row gtr-uniform gtr-50">
+						<div class="col-8 col-12-small">
+							<select name="show_id" aria-label="Show" required>
+								<option value="">Choose a show…</option>
+<?php foreach ($shows as $show): ?>
+								<option value="<?= (int)$show['id'] ?>"<?= $current && $current['id'] == $show['id'] ? ' selected' : '' ?>><?= e($show['name']) ?></option>
+<?php endforeach; ?>
+							</select>
+						</div>
+						<div class="col-4 col-12-small">
+							<input type="submit" class="primary fit" value="<?= $live ? 'Switch show' : 'Queue show' ?>" />
+						</div>
+					</div>
+				</form>
+
+<?php if (!$live && $current): ?>
+				<form method="post" action="index.php">
+					<?= csrfField() ?>
+					<input type="hidden" name="action" value="clear_queue" />
+					<input type="submit" class="small" value="Clear queued show" />
+				</form>
+<?php endif; ?>
 <?php
 adminFooter();