Add standalone weather widget (current/hourly/daily/multi-city, pluggable providers)

New widget type with four display modes -- current conditions, an
hourly forecast strip, a multi-day forecast, and several cities' current
day side by side -- backed by a pluggable provider registry (app/weather/,
mirroring the app/widgets/ dispatch pattern): Open-Meteo (worldwide) and
NWS (US-only) both wired up now, Environment Canada documented as the
next one to add given its more involved station/grid-lookup API.

The calendar widget's existing embedded weather strip is untouched and
still Open-Meteo-only; this lifts the same underlying icon-drawing
primitives (now shared via app/weather_render.py, calendar_render.py
still imports draw_weather_row unchanged) into a widget that can be
placed and sized on its own. Icons are redrawn in the panel's actual ink
colors (yellow sun/bolt, blue rain/snow) instead of flat black, and
build_multi_city's icon/font sizing now scales with how many cities need
to fit rather than the box's height alone -- both fixed after catching
them via live browser verification, along with a mode-switch cache-shape
crash and a mobile-width dialog overflow.

New WeatherWidgetConfig table (migration 24), grid footprint, widget
module, common.py fetch/cache helper, router endpoints (location set/
clear, city add/remove, preview), dialog template + JS, and full test
coverage (providers, widget render, HTTP endpoints, migration replay).
docs/widgets.md and CLAUDE.md's TODO updated accordingly.

server/app/templates/_widget_dialog_weather.html

@@ -0,0 +1,81 @@
+<h2 class="dialog-title">Weather widget</h2>
+
+<section class="card">
+  <h2 class="card-title">Display</h2>
+  <form id="weather-config-form">
+    <label>Mode
+      <select id="weather_mode">
+        <option value="current" {% if weather_cfg.mode == "current" %}selected{% endif %}>Current conditions</option>
+        <option value="hourly" {% if weather_cfg.mode == "hourly" %}selected{% endif %}>Hourly forecast</option>
+        <option value="daily" {% if weather_cfg.mode == "daily" %}selected{% endif %}>Multi-day forecast</option>
+        <option value="multi_city" {% if weather_cfg.mode == "multi_city" %}selected{% endif %}>Multiple cities</option>
+      </select>
+    </label>
+    <label>Weather source
+      <select id="weather_provider">
+        {% for value, label in weather_provider_labels.items() %}
+          <option value="{{ value }}" {% if weather_cfg.provider == value %}selected{% endif %}>{{ label }}</option>
+        {% endfor %}
+      </select>
+    </label>
+    <p class="sub" style="margin-top: 4px;">National Weather Service only covers US locations.</p>
+    <label>Units
+      <select id="weather_units">
+        <option value="fahrenheit" {% if weather_cfg.units == "fahrenheit" %}selected{% endif %}>Fahrenheit</option>
+        <option value="celsius" {% if weather_cfg.units == "celsius" %}selected{% endif %}>Celsius</option>
+      </select>
+    </label>
+    <div id="weather-hourly-interval-row">
+      <label>Hours between ticks
+        <select id="weather_hourly_interval_hours">
+          {% for hours in (3, 4, 6, 12) %}
+            <option value="{{ hours }}" {% if weather_cfg.hourly_interval_hours == hours %}selected{% endif %}>{{ hours }}</option>
+          {% endfor %}
+        </select>
+      </label>
+    </div>
+    <div id="weather-daily-days-row">
+      <label>Days to show
+        <input type="number" id="weather_daily_days" min="1" max="14" value="{{ weather_cfg.daily_days }}">
+      </label>
+    </div>
+    <button type="submit">Save</button>
+  </form>
+</section>
+
+<section class="card" id="weather-location-section" style="margin-top: 20px;">
+  <h2 class="card-title">Location</h2>
+  <p class="sub" id="weather-location-current">
+    {% if weather_cfg.city_label %}Currently: {{ weather_cfg.city_label }}{% else %}No location set yet.{% endif %}
+  </p>
+  <div class="checkbox-row" style="flex-wrap: wrap;">
+    <input type="text" id="weather-location-input" placeholder="e.g. Portland, OR" style="margin-top: 0; flex: 1 1 160px;">
+    <button type="button" class="btn-inline" id="weather-location-set">Set</button>
+    <button type="button" class="btn-inline secondary" id="weather-location-clear">Clear</button>
+  </div>
+</section>
+
+<section class="card" id="weather-cities-section" style="margin-top: 20px;">
+  <h2 class="card-title">Cities</h2>
+  <ul class="calendar-user-list" id="weather-widget-city-list">
+    {% for c in weather_cfg.cities or [] %}
+      <li class="checkbox-row" style="justify-content: space-between; margin-top: 6px;">
+        <span>{{ c.label }}</span>
+        <button type="button" class="btn-inline secondary weather-widget-city-remove" data-label="{{ c.label }}">Remove</button>
+      </li>
+    {% else %}
+      <li class="sub" id="weather-widget-city-empty">No cities added yet.</li>
+    {% endfor %}
+  </ul>
+  <div class="checkbox-row" style="margin-top: 10px;">
+    <input type="text" id="weather-widget-city-input" placeholder="e.g. Portland, OR" style="margin-top: 0; flex: 1;">
+    <button type="button" class="btn-inline" id="weather-widget-city-add">Add</button>
+  </div>
+</section>
+
+<section class="card" style="margin-top: 20px;">
+  <h2 class="card-title">Preview</h2>
+  <p class="sub">How this widget currently renders.</p>
+  <img class="preview-img" id="weather-preview" alt="Weather preview">
+  <button type="button" class="secondary" id="weather-preview-refresh">Refresh now</button>
+</section>