Fix manual switch reverting instantly, add weather forecast

- scheduler: "Show X now" was a true one-shot -- reverted on the very next
  5s tick, causing the flash-to-X-then-flash-back-to-clock behavior. Now
  pins for 5 minutes (still preemptable by Navidrome priority, which stays
  authoritative). Added a "Resume automatic" action/button and status
  display showing what's pinned and until when.
- weather: daily forecast strip (3/5/7 days, selectable in settings) below
  current conditions, via Open-Meteo's daily= params in the same request.
  Fixed a bad symbol choice along the way -- DejaVu Sans has no glyph for
  the partly-cloudy emoji, was rendering as a tofu box; swapped to the
  plain cloud symbol, verified glyph coverage for the whole WMO code table.

web/templates/index.html

@@ -22,6 +22,10 @@
       <span class="badge {{ 'on' if rotation.enabled else 'off' }}">{{ "on" if rotation.enabled else "off" }}</span>
       {{ rotation.screens | join(" → ") }} (every {{ rotation.interval_minutes }} min)
     </dd>
+    {% if status.manual_screen %}
+    <dt>Manual pin</dt>
+    <dd><span class="badge on">{{ screens[status.manual_screen].display_name }}</span> until {{ status.manual_until }}</dd>
+    {% endif %}
   </dl>
 </div>
 
@@ -36,6 +40,11 @@
       <button class="secondary" type="submit">Show {{ screen.display_name }}</button>
     </form>
     {% endfor %}
+    {% if status.manual_screen %}
+    <form class="inline" method="post" action="{{ url_for('resume_rotation') }}">
+      <button class="secondary" type="submit">Resume automatic</button>
+    </form>
+    {% endif %}
   </div>
 </div>
 {% endblock %}