feat(ui): shared |bytes |rate |duration |ago filters and status_class from Settings → Thresholds (#5093)

#5093 "Shared format filters and status_class driven by Settings → Thresholds".

- steward/core/formatting.py: human_bytes (binary units), human_rate,
  human_duration (two largest units), ago (a <time> titled with the absolute
  UTC time) and status_class(value, kind, thresholds) -> ok/warn/crit/unknown,
  which raises on a kind the thresholds don't name.
- app.py registers them as the bytes, rate, duration and ago filters and the
  status_class global; threshold_style is now graded by status_class (and caps
  its weight at 500).
- Replaces the copies: docker's _human_bytes/_human_uptime, core alerts'
  _duration, the host-agent fmt_bps/fmt_bytes macros, the Traefik and UniFi
  byte-rate arithmetic, the swarm-failures ago macro and two uptime spans.
- Tests: a table per helper, and every template compiled against the app's
  filters, so an unknown filter fails CI rather than a page.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

plugins/unifi/templates/unifi/widget.html

@@ -37,16 +37,12 @@
     <span>
       <span style="color:var(--text-muted);">&#8595;</span>
       {% set bps = latest_wan.rx_bytes_rate %}
-      {% if bps >= 1048576 %}{{ "%.1f"|format(bps / 1048576) }}MB/s
-      {% elif bps >= 1024 %}{{ "%.0f"|format(bps / 1024) }}KB/s
-      {% else %}{{ "%.0f"|format(bps) }}B/s{% endif %}
+      {{ bps|rate }}
     </span>
     <span>
       <span style="color:var(--text-muted);">&#8593;</span>
       {% set bps = latest_wan.tx_bytes_rate %}
-      {% if bps >= 1048576 %}{{ "%.1f"|format(bps / 1048576) }}MB/s
-      {% elif bps >= 1024 %}{{ "%.0f"|format(bps / 1024) }}KB/s
-      {% else %}{{ "%.0f"|format(bps) }}B/s{% endif %}
+      {{ bps|rate }}
     </span>
     {% endif %}
   </div>
@@ -76,14 +72,10 @@
       {% set total_bps = c.tx_rate + c.rx_rate %}
       <span style="color:var(--text-muted);">&#8595;</span>
       {% set rx = c.rx_rate %}
-      {% if rx >= 1048576 %}{{ "%.1f"|format(rx / 1048576) }}M
-      {% elif rx >= 1024 %}{{ "%.0f"|format(rx / 1024) }}K
-      {% else %}{{ "%.0f"|format(rx) }}B{% endif %}
+      {{ rx|rate }}
       <span style="color:var(--text-muted);margin-left:0.4rem;">&#8593;</span>
       {% set tx = c.tx_rate %}
-      {% if tx >= 1048576 %}{{ "%.1f"|format(tx / 1048576) }}M
-      {% elif tx >= 1024 %}{{ "%.0f"|format(tx / 1024) }}K
-      {% else %}{{ "%.0f"|format(tx) }}B{% endif %}
+      {{ tx|rate }}
     </div>
   </div>
   {% endfor %}