Add Jinja2 web UI with Bootstrap 5 dark theme

- app/templates/: base layout with sidebar nav + 6 pages
  (dashboard, printers, jobs, filaments, todos, pricing)
- app/routers/ui.py: HTML routes querying the DB live
- API routes moved to /api/* prefix
- requirements: jinja2, python-multipart

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

app/templates/pricing.html

@@ -0,0 +1,30 @@
+{% extends "base.html" %}
+{% block title %}Pricing — POPS{% endblock %}
+
+{% block content %}
+<h5 class="text-white mb-4">Pricing Configuration</h5>
+{% if configs %}
+<div class="row g-3">
+{% for c in configs %}
+<div class="col-md-6 col-xl-4">
+  <div class="card p-3">
+    <div class="d-flex justify-content-between align-items-start mb-3">
+      <span class="fw-semibold text-white">{{ c.name }}</span>
+      <span class="text-secondary small">from {{ c.valid_from.strftime('%d.%m.%Y') }}</span>
+    </div>
+    <table class="table table-dark table-sm mb-0" style="font-size:.85rem">
+      <tbody>
+        <tr><td class="text-secondary border-0">Electricity</td><td class="text-end border-0">€ {{ "%.4f"|format(c.electricity_kwh_eur) }} / kWh</td></tr>
+        <tr><td class="text-secondary">Printer draw</td><td class="text-end">{{ c.printer_watt }} W</td></tr>
+        <tr><td class="text-secondary">Hourly rate</td><td class="text-end">€ {{ "%.2f"|format(c.hourly_rate_eur) }} / h</td></tr>
+        <tr><td class="text-secondary">Markup</td><td class="text-end">{{ c.markup_percent }} %</td></tr>
+      </tbody>
+    </table>
+  </div>
+</div>
+{% endfor %}
+</div>
+{% else %}
+<div class="card"><div class="card-body text-secondary">No pricing config yet.</div></div>
+{% endif %}
+{% endblock %}