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_weather.html

@@ -1,16 +1,37 @@
 {% extends "base.html" %}
 {% block content %}
 <h1>Weather</h1>
-<p style="font-size:0.85rem;color:#666">Uses Open-Meteo (no API key needed) &mdash; just the coordinates for your location.</p>
+
+{% if error %}
+<div class="toast error">{{ error }}</div>
+{% endif %}
+
 <form method="post">
-  <div class="field">
-    <label for="latitude">Latitude</label>
-    <input type="text" id="latitude" name="latitude" value="{{ settings.latitude if settings.latitude is not none else '' }}" placeholder="e.g. 52.52">
+  <div class="card">
+    <div class="section-label">Location</div>
+    <p class="hint" style="margin: -0.25rem 0 1rem;">Uses Open-Meteo &mdash; no API key needed.</p>
+    <div class="field">
+      <label for="city">City</label>
+      <input type="text" id="city" name="city" placeholder="e.g. Berlin">
+      {% if settings.city %}
+      <p class="hint">Currently: {{ settings.city }} ({{ settings.latitude }}, {{ settings.longitude }})</p>
+      {% endif %}
+    </div>
   </div>
-  <div class="field">
-    <label for="longitude">Longitude</label>
-    <input type="text" id="longitude" name="longitude" value="{{ settings.longitude if settings.longitude is not none else '' }}" placeholder="e.g. 13.40">
+
+  <div class="card">
+    <div class="section-label">Or enter coordinates manually</div>
+    <p class="hint" style="margin: -0.25rem 0 1rem;">Leave the city field above empty to use these instead.</p>
+    <div class="field">
+      <label for="latitude">Latitude</label>
+      <input type="text" id="latitude" name="latitude" value="{{ settings.latitude if settings.latitude is not none else '' }}" placeholder="e.g. 52.52">
+    </div>
+    <div class="field">
+      <label for="longitude">Longitude</label>
+      <input type="text" id="longitude" name="longitude" value="{{ settings.longitude if settings.longitude is not none else '' }}" placeholder="e.g. 13.40">
+    </div>
   </div>
+
   <button type="submit">Save</button>
 </form>
 {% endblock %}