Add brand autocomplete dropdown to battery add and device install forms

Uses HTML datalist populated from distinct brands in the battery table.
Removed autocomplete="off" which suppresses datalist in Chrome/Chromium.

templates/battery_add.html

@@ -9,7 +9,10 @@
     <div class="form-group">
       <label for="brand">Brand <span class="text-danger">*</span></label>
       <input type="text" id="brand" name="brand" value="{{ form_brand|default('') }}"
-             placeholder="e.g. Panasonic Eneloop" required>
+             placeholder="e.g. Panasonic Eneloop" list="brand-list" required>
+      <datalist id="brand-list">
+        {% for b in brands|default([]) %}<option value="{{ b }}">{% endfor %}
+      </datalist>
     </div>
 
     <div class="form-group">

templates/device_detail.html

@@ -29,12 +29,16 @@
   <h2>Install Batteries</h2>
   {% set free_slots = device.battery_slots - device.installed_count() %}
   <p class="text-muted" style="margin-bottom:0.75rem;">{{ free_slots }} slot(s) free</p>
+  <datalist id="brand-list">
+    {% for b in brands|default([]) %}<option value="{{ b }}">{% endfor %}
+  </datalist>
   <form method="post" action="{{ url_for('device_install', device_id=device.id) }}">
     <div style="display:grid;grid-template-columns:1fr auto;gap:0.4rem;max-width:360px;align-items:center;margin-bottom:0.75rem;">
       <span style="font-weight:600;font-size:0.85rem;color:#64748b;">Brand</span>
       <span style="font-weight:600;font-size:0.85rem;color:#64748b;">Qty</span>
       {% for _ in range(4) %}
-      <input type="text" name="brand[]" placeholder="e.g. Eneloop" style="padding:0.3rem 0.5rem;">
+      <input type="text" name="brand[]" placeholder="e.g. Eneloop"
+             list="brand-list" style="padding:0.3rem 0.5rem;">
       <input type="number" name="qty[]" value="0" min="0"
              style="padding:0.3rem 0.5rem;width:4rem;text-align:center;">
       {% endfor %}