Feature: HTMX + Jinja2 Frontend ersetzt Next.js komplett

- Kein Node.js, kein npm, kein Build-Schritt mehr
- HTMX 2.0.4 + PicoCSS 2 vendored in backend/static/
- Jinja2 Templates für alle 9 Seiten (Dashboard, ZFS, Snapshots,
  Shares, Identities, Logs, Services, Navigator, Login)
- HTMX Fragments für Live-Updates (30s Polling Dashboard)
- JWT als httpOnly Cookie statt localStorage
- Disk Usage zeigt TB/PB korrekt (Jinja2 serverseitig formatiert)
- Update-safe: nur Python-Deps, keine npm-Abhängigkeiten

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

backend/templates/fragments/net_traffic.html

@@ -0,0 +1,23 @@
+{% macro fmt_bytes(b) %}
+  {%- if b < 1048576 %}{{ "%.1f"|format(b/1024) }} KB
+  {%- elif b < 1073741824 %}{{ "%.1f"|format(b/1048576) }} MB
+  {%- else %}{{ "%.2f"|format(b/1073741824) }} GB
+  {%- endif %}
+{%- endmacro %}
+
+<div style="display:grid;grid-template-columns:repeat(auto-fill,minmax(200px,1fr));gap:1rem">
+{% for iface in interfaces %}
+  {% if iface.name not in ['lo'] %}
+  <article style="margin:0;padding:1rem">
+    <strong>{{ iface.name }}</strong>
+    <table style="margin:0.5rem 0;font-size:0.85rem">
+      <tr><td style="color:var(--pico-muted-color)">RX</td><td><strong>{{ fmt_bytes(iface.rx_bytes) }}</strong></td><td style="color:var(--pico-muted-color)">{{ "{:,}".format(iface.rx_packets) }} pkt</td></tr>
+      <tr><td style="color:var(--pico-muted-color)">TX</td><td><strong>{{ fmt_bytes(iface.tx_bytes) }}</strong></td><td style="color:var(--pico-muted-color)">{{ "{:,}".format(iface.tx_packets) }} pkt</td></tr>
+      {% if iface.rx_drops > 0 or iface.tx_drops > 0 %}
+      <tr><td colspan="3" style="color:#fca5a5;font-size:0.75rem">&#9888; {{ iface.rx_drops + iface.tx_drops }} drops</td></tr>
+      {% endif %}
+    </table>
+  </article>
+  {% endif %}
+{% endfor %}
+</div>