Initial commit: Flask battery tracker app

- Flask + SQLAlchemy (MariaDB-compatible schema) battery tracking web app
- 40 pre-seeded batteries (Eneloop, BONAI, Energizer NiMH) across 5 devices
- Business rules: block retired assignment, brand-mix warnings, capacity checks
- Mobile-friendly Jinja2 templates with inline CSS
- waitress WSGI server via systemd user service (sbin/install-service.sh)
- SQLite → MariaDB migration script (migrate_to_mariadb.py)
- 26 passing acceptance tests (pytest + Flask test client)

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

templates/device_list.html

@@ -0,0 +1,58 @@
+{% extends "base.html" %}
+{% block title %}Devices — Battery Tracker{% endblock %}
+
+{% block content %}
+<h1>Devices</h1>
+
+<div class="card">
+  <div class="table-wrap">
+    <table>
+      <thead>
+        <tr>
+          <th>Name</th>
+          <th>Slots</th>
+          <th>Installed</th>
+          <th>Brands</th>
+          <th>Actions</th>
+        </tr>
+      </thead>
+      <tbody>
+        {% for d in devices %}
+        <tr>
+          <td><a href="{{ url_for('device_detail', device_id=d.id) }}"><strong>{{ d.name }}</strong></a></td>
+          <td>{{ d.battery_slots }}</td>
+          <td>
+            {{ d.installed_count() }} / {{ d.battery_slots }}
+            {% if d.installed_count() >= d.battery_slots %}
+              <span class="badge badge-retired">Full</span>
+            {% endif %}
+          </td>
+          <td>
+            {% set brands = d.installed_brands() %}
+            {% if brands %}
+              {{ brands|join(', ') }}
+              {% if d.has_mixed_brands() %}
+                <span class="badge badge-warning">⚠ mixed</span>
+              {% endif %}
+            {% else %}
+              <span class="text-muted">—</span>
+            {% endif %}
+          </td>
+          <td style="white-space:nowrap;">
+            <a class="btn btn-sm btn-secondary" href="{{ url_for('device_detail', device_id=d.id) }}">View</a>
+            <form class="inline" method="post" action="{{ url_for('device_delete', device_id=d.id) }}"
+                  onsubmit="return confirm('Delete {{ d.name }}? All installed batteries will be unassigned.');">
+              <button class="btn btn-sm btn-danger" type="submit">Delete</button>
+            </form>
+          </td>
+        </tr>
+        {% else %}
+        <tr><td colspan="5" class="text-muted" style="text-align:center;padding:1rem;">No devices yet. <a href="{{ url_for('device_add') }}">Add one.</a></td></tr>
+        {% endfor %}
+      </tbody>
+    </table>
+  </div>
+</div>
+
+<a class="btn btn-primary" href="{{ url_for('device_add') }}">+ Add Device</a>
+{% endblock %}