Map tab: much bigger map with its own remembered view

- Map fills the screen (was a 56vh strip); timeline and details sit below it
- No longer snaps back to the main-page radar's location/zoom on every refresh or tab switch;
  starts as a wider regional view, remembers pan/zoom, and recentres only when the location changes
- New 'My location' button

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

app/public/index.html

@@ -259,6 +259,7 @@
             <option value="light">Light</option>
             <option value="satellite">Satellite</option>
           </select>
+          <button id="map-recenter-btn" class="map-recenter" type="button" title="Back to my location">📍 My location</button>
           <button id="map-fullscreen-btn" class="radar-btn radar-fs-btn" title="Fullscreen">⛶</button>
         </div>
         
@@ -351,7 +352,7 @@
 
       <!-- Main Map -->
       <div class="unified-map-shell">
-        <div id="unified-map" class="unified-map-container" style="height:56vh; min-height:420px;"></div>
+        <div id="unified-map" class="unified-map-container"></div>
         <div class="map-overlay-readouts" id="map-overlay-readouts">
           <span class="map-readout-chip" id="overlay-temp">Temp --</span>
           <span class="map-readout-chip" id="overlay-aqi">AQI --</span>