Add OpenWeatherMap weather forecasts. Closes #48

Show 8-day Bristol home weather on the index and weekends pages.
Show destination weather per day on the trip list and trip page.
Cache forecasts in ~/lib/data/weather/ and refresh via update.py.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

templates/weekends.html

@@ -12,8 +12,10 @@
         <th class="text-end">Date</th>
         <th>Saturday</th>
         <th>Saturday Location</th>
+        <th>Saturday Weather</th>
         <th>Sunday</th>
         <th>Sunday Location</th>
+        <th>Sunday Weather</th>
       </tr>
     </thead>
     <tbody>
@@ -51,6 +53,13 @@
           {{ city }}, {{ country.flag }} {{ country.name }}
         {% endif %}
       </td>
+      {% if extra_class %}<td class="{{ extra_class|trim }}">{% else %}<td>{% endif %}
+        {% set w = weekend[day + '_weather'] %}
+        {% if w %}
+          <img src="https://openweathermap.org/img/wn/{{ w.icon }}.png" alt="{{ w.status }}" title="{{ w.detailed_status }}" width="25" height="25">
+          {{ w.temp_min }}–{{ w.temp_max }}°C
+        {% endif %}
+      </td>
     {% endfor %}
     </tr>
   {% endfor %}