Add storage location field to battery with dynamic dropdown

Dropdown populated from existing distinct storage locations,
with 'New location...' option revealing a text input.

templates/battery_detail.html

@@ -66,6 +66,7 @@
     {% endif %}
     {{ meta_row("Charge Cycles", battery.charge_cycles) }}
     {{ meta_row("Purchase Date", battery.purchase_date) }}
+    {{ meta_row("Storage", battery.storage_location) }}
     {% if battery.notes %}
     <tr>
       <td style="padding:0.3rem 1rem 0.3rem 0;font-weight:600;color:#64748b;border:none;">Notes</td>
@@ -142,6 +143,21 @@
 
     </div>
 
+    <div class="form-group">
+      <label>Storage Location</label>
+      <select id="storage-select" onchange="metaSelectChanged(this,'storage_location')">
+        <option value="">— none —</option>
+        {% for loc in storage_locations|default([]) %}
+        <option value="{{ loc }}" {% if battery.storage_location == loc %}selected{% endif %}>{{ loc }}</option>
+        {% endfor %}
+        <option value="__new__" {% if battery.storage_location and battery.storage_location not in storage_locations|default([]) %}selected{% endif %}>➕ New location…</option>
+      </select>
+      <input type="text" id="storage_location" name="storage_location"
+             value="{{ battery.storage_location or '' }}"
+             placeholder="e.g. Drawer 2, Toolbox, Shelf A"
+             style="display:{% if battery.storage_location and battery.storage_location not in storage_locations|default([]) %}''{% else %}none{% endif %};margin-top:0.4rem;">
+    </div>
+
     <div class="form-group">
       <label for="notes">Notes</label>
       <textarea id="notes" name="notes" placeholder="No notes yet…">{{ battery.notes or '' }}</textarea>