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_add.html

@@ -0,0 +1,32 @@
+{% extends "base.html" %}
+{% block title %}Add Device — Battery Tracker{% endblock %}
+
+{% block content %}
+<h1>Add Device</h1>
+
+<div class="card">
+  <form method="post" action="{{ url_for('device_add') }}">
+    <div class="form-group">
+      <label for="name">Device Name <span class="text-danger">*</span></label>
+      <input type="text" id="name" name="name" value="{{ form_name|default('') }}"
+             placeholder="e.g. Game Controller" required>
+    </div>
+
+    <div class="form-group">
+      <label for="battery_slots">Battery Slots <span class="text-danger">*</span></label>
+      <input type="number" id="battery_slots" name="battery_slots"
+             value="{{ form_slots|default(1) }}" min="1" required>
+    </div>
+
+    <div class="form-group">
+      <label for="notes">Notes</label>
+      <textarea id="notes" name="notes" placeholder="Optional notes…">{{ form_notes|default('') }}</textarea>
+    </div>
+
+    <div class="form-actions">
+      <button class="btn btn-primary" type="submit">Add Device</button>
+      <a class="btn btn-secondary" href="{{ url_for('device_list') }}">Cancel</a>
+    </div>
+  </form>
+</div>
+{% endblock %}