Landscape orientation, redesigned web UI, rotation on/off + minutes, weather by city name

- Panel is mounted sideways: render landscape (600x400), rotate to the
  panel's native portrait orientation right before writing to hardware.
- Web UI: card-based layout, dark mode, active nav highlighting, save
  confirmation toasts, error banners.
- Rotation: separate enabled/disabled toggle (off pins to the first screen
  in the list) and the interval is now in minutes instead of raw seconds.
  Migrates existing config.json from the old interval_seconds field.
- Weather: type a city name instead of hunting down coordinates, resolved
  via Open-Meteo's free geocoding API. Manual lat/long still available as
  a fallback.

web/templates/settings_rotation.html

@@ -3,25 +3,35 @@
 <h1>Rotation</h1>
 
 <form method="post">
-  <div class="field">
-    <label>Navidrome takes over when music plays</label>
+  <div class="card">
+    <div class="section-label">Priority</div>
     <label class="checkbox">
       <input type="checkbox" name="navidrome_priority" {{ "checked" if navidrome_priority }}>
-      Show Navidrome immediately whenever something is playing, regardless of rotation
+      Navidrome takes over immediately whenever something is playing, regardless of rotation
     </label>
   </div>
 
-  <div class="field">
-    <label for="screens">Rotation order (used when Navidrome isn't playing, or if priority is off)</label>
-    <input type="text" id="screens" name="screens" value="{{ rotation.screens | join(', ') }}" placeholder="clock, weather">
-    <p style="font-size:0.8rem;color:#666">
-      Comma-separated, in order. Available: {{ screens.keys() | join(', ') }}.
+  <div class="card">
+    <div class="section-label">Rotation</div>
+    <label class="checkbox">
+      <input type="checkbox" name="rotation_enabled" {{ "checked" if rotation.enabled }}>
+      Enabled -- cycle through the screens below on a timer
+    </label>
+    <p class="hint" style="margin: 0.6rem 0 1.1rem;">
+      Off just pins to the first screen in the order below (still shown when
+      Navidrome priority is on but nothing's playing). "Show X now" buttons on
+      the Status page still work either way, they just don't stick past the
+      next check.
     </p>
-  </div>
-
-  <div class="field">
-    <label for="interval_seconds">Rotation interval (seconds)</label>
-    <input type="number" id="interval_seconds" name="interval_seconds" value="{{ rotation.interval_seconds }}" min="10">
+    <div class="field">
+      <label for="screens">Order</label>
+      <input type="text" id="screens" name="screens" value="{{ rotation.screens | join(', ') }}" placeholder="clock, weather">
+      <p class="hint">Comma-separated, in order. Available: {{ screens.keys() | join(', ') }}.</p>
+    </div>
+    <div class="field">
+      <label for="interval_minutes">Switch every (minutes)</label>
+      <input type="number" id="interval_minutes" name="interval_minutes" value="{{ rotation.interval_minutes }}" min="1">
+    </div>
   </div>
 
   <button type="submit">Save</button>