Add inline assign from dashboard, specific battery picker on device, dynamic install rows

- Dashboard: replace Assign link with device dropdown + arrow button for
  quick inline assignment without leaving the page
- Device detail: replace hardcoded 4-row install form with 1 row + '+ Add
  brand' button that clones rows dynamically
- Device detail: add 'Install Specific Battery' card with dropdown of all
  available batteries (label, brand, size, notes) via new /device/<id>/install-one route
- Tests: 4 new acceptance tests covering dashboard quick-assign and
  install-one, including capacity enforcement on both paths (39 total)

templates/dashboard.html

@@ -167,7 +167,18 @@
               <a class="btn btn-sm btn-secondary" href="{{ url_for('battery_detail', battery_id=b.id) }}">View</a>
 
               {% if b.is_available() %}
-                <a class="btn btn-sm btn-primary" href="{{ url_for('battery_assign', battery_id=b.id) }}">Assign</a>
+                <select id="qas-{{ b.id }}"
+                        style="padding:0.2rem 0.3rem;font-size:0.8rem;border:1px solid #cbd5e1;border-radius:4px;max-width:110px;vertical-align:middle;">
+                  <option value="">— assign —</option>
+                  {% for d in devices %}
+                  <option value="{{ d.id }}"
+                    {% if d.installed_count() >= d.battery_slots %}disabled{% endif %}>
+                    {{ d.name }} ({{ d.installed_count() }}/{{ d.battery_slots }})
+                  </option>
+                  {% endfor %}
+                </select>
+                <button type="button" class="btn btn-sm btn-primary"
+                        onclick="quickAssign('{{ url_for('battery_assign', battery_id=b.id) }}', {{ b.id }})">→</button>
               {% endif %}
 
               {% if b.is_installed() %}
@@ -249,6 +260,18 @@ function applyFilters() {
   updateToolbar();
 }
 
+function quickAssign(action, batteryId) {
+  var sel = document.getElementById('qas-' + batteryId);
+  if (!sel.value) { sel.focus(); return; }
+  var f = document.createElement('form');
+  f.method = 'post'; f.action = action;
+  var inp = document.createElement('input');
+  inp.type = 'hidden'; inp.name = 'device_id'; inp.value = sel.value;
+  f.appendChild(inp);
+  document.body.appendChild(f);
+  f.submit();
+}
+
 function resetFilters() {
   ['filter-status','filter-brand','filter-size','filter-storage'].forEach(function(id) {
     document.getElementById(id).value = '';

templates/device_detail.html

@@ -30,41 +30,51 @@
   {% set free_slots = device.battery_slots - device.installed_count() %}
   <p class="text-muted" style="margin-bottom:0.75rem;">{{ free_slots }} slot(s) free</p>
   <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:400px;align-items:start;margin-bottom:0.75rem;">
+    <div id="install-grid" style="display:grid;grid-template-columns:1fr auto;gap:0.4rem;max-width:400px;align-items:start;margin-bottom:0.5rem;">
       <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 i in range(1, 5) %}
-      <div>
-        <select onchange="brandSelectChanged(this, 'brand-{{ i }}')">
-          <option value="">— select —</option>
-          {% for b in brands|default([]) %}
-          <option value="{{ b }}">{{ b }}</option>
-          {% endfor %}
-          <option value="__new__">➕ New brand…</option>
-        </select>
-        <input type="text" id="brand-{{ i }}" name="brand[]" value=""
-               placeholder="Type brand name"
-               style="display:none;margin-top:0.3rem;padding:0.3rem 0.5rem;">
+      <div class="install-row-pair" style="display:contents;">
+        <div>
+          <select onchange="brandSelectChanged(this)">
+            <option value="">— select —</option>
+            {% for b in brands|default([]) %}
+            <option value="{{ b }}">{{ b }}</option>
+            {% endfor %}
+            <option value="__new__">➕ New brand…</option>
+          </select>
+          <input type="text" name="brand[]" value=""
+                 placeholder="Type brand name"
+                 style="display:none;margin-top:0.3rem;padding:0.3rem 0.5rem;">
+        </div>
+        <input type="number" name="qty[]" value="0" min="0"
+               style="padding:0.3rem 0.5rem;width:4rem;text-align:center;">
       </div>
-      <input type="number" name="qty[]" value="0" min="0"
-             style="padding:0.3rem 0.5rem;width:4rem;text-align:center;">
-      {% endfor %}
     </div>
+    <button type="button" class="btn btn-sm btn-secondary" onclick="addInstallRow()" style="margin-bottom:0.75rem;">+ Add brand</button>
+    <br>
     <button class="btn btn-primary" type="submit">Install</button>
   </form>
 
 <script>
-function brandSelectChanged(sel, inputId) {
-  var input = document.getElementById(inputId);
-  if (sel.value === '__new__' || sel.value === '') {
-    input.style.display = sel.value === '__new__' ? '' : 'none';
-    input.value = '';
-    if (sel.value === '__new__') input.focus();
+function brandSelectChanged(sel) {
+  var input = sel.nextElementSibling;
+  if (sel.value === '__new__') {
+    input.style.display = ''; input.value = ''; input.focus();
   } else {
     input.style.display = 'none';
-    input.value = sel.value;
+    input.value = (sel.value === '') ? '' : sel.value;
   }
 }
+function addInstallRow() {
+  var grid = document.getElementById('install-grid');
+  var tmpl = grid.querySelector('.install-row-pair');
+  var clone = tmpl.cloneNode(true);
+  clone.querySelector('select').value = '';
+  clone.querySelector('input[type=text]').style.display = 'none';
+  clone.querySelector('input[type=text]').value = '';
+  clone.querySelector('input[type=number]').value = '0';
+  grid.appendChild(clone);
+}
 </script>
 </div>
 
@@ -98,6 +108,28 @@ function brandSelectChanged(sel, inputId) {
   {% endif %}
 </div>
 
+<div class="card">
+  <h2>Install Specific Battery</h2>
+  {% if available_batteries %}
+  <form method="post" action="{{ url_for('device_install_one', device_id=device.id) }}">
+    <div class="form-group">
+      <label for="battery_id">Battery</label>
+      <select name="battery_id" id="battery_id">
+        <option value="">— select —</option>
+        {% for b in available_batteries %}
+        <option value="{{ b.id }}">{{ b.label }} — {{ b.brand }}
+          {%- if b.size %} {{ b.size }}{% endif %}
+          {%- if b.notes %} ({{ b.notes }}){% endif %}</option>
+        {% endfor %}
+      </select>
+    </div>
+    <button class="btn btn-primary" type="submit">Install</button>
+  </form>
+  {% else %}
+    <p class="text-muted">No available batteries.</p>
+  {% endif %}
+</div>
+
 <div class="card">
   <h2>Delete Device</h2>
   <p style="margin-bottom:1rem;" class="text-muted">