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/host_agent/templates/widget_table.html

@@ -13,21 +13,13 @@
   <div style="line-height:0;height:16px;">{{ svg | safe }}</div>
 </div>
 {% endmacro %}
-{# Human-readable throughput, matching the host-detail page. #}
-{% macro fmt_bps(v) %}
-{%- if v is none -%}—
-{%- elif v >= 1048576 -%}{{ "%.1f"|format(v / 1048576) }} MB/s
-{%- elif v >= 1024 -%}{{ "%.1f"|format(v / 1024) }} KB/s
-{%- else -%}{{ "%.0f"|format(v) }} B/s
-{%- endif -%}
-{% endmacro %}
 {# Two-line down/up (or read/write) throughput cell. #}
 {% macro io_cell(label, down_sym, down_val, up_sym, up_val, title="") %}
 <div style="min-width:80px;flex:0 0 auto;" title="{{ title }}">
   <div style="font-size:0.62rem;color:var(--text-dim);text-transform:uppercase;letter-spacing:0.03em;">{{ label }}</div>
   <div style="font-size:0.72rem;font-variant-numeric:tabular-nums;line-height:1.3;">
-    <div>{{ down_sym }} {{ fmt_bps(down_val) }}</div>
-    <div>{{ up_sym }} {{ fmt_bps(up_val) }}</div>
+    <div>{{ down_sym }} {{ down_val|rate }}</div>
+    <div>{{ up_sym }} {{ up_val|rate }}</div>
   </div>
 </div>
 {% endmacro %}