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>

tests/plugins/docker/test_routes.py

@@ -41,21 +41,9 @@ def test_container_log_views_defined():
     assert callable(r.container_logs_lines)
 
 
-def test_human_bytes_formats_binary_units():
-    assert r._human_bytes(None) == "—"
-    assert r._human_bytes(0) == "0 B"
-    assert r._human_bytes(512) == "512 B"
-    assert r._human_bytes(1024) == "1.0 KiB"
-    assert r._human_bytes(1536) == "1.5 KiB"
-    assert r._human_bytes(1024 ** 2) == "1.0 MiB"
-    assert r._human_bytes(int(1.5 * 1024 ** 3)) == "1.5 GiB"
-    assert r._human_bytes(1024 ** 4) == "1.0 TiB"
-
-
-def test_human_uptime_compact():
+def test_uptime_is_the_shared_duration_or_none():
     from datetime import datetime, timedelta, timezone
     now = datetime.now(timezone.utc)
-    assert r._human_uptime(None) is None
-    assert r._human_uptime(now - timedelta(minutes=8)).endswith("m")
-    assert "h" in r._human_uptime(now - timedelta(hours=5, minutes=12))
-    assert "d" in r._human_uptime(now - timedelta(days=3, hours=4))
+    assert r._uptime(None) is None
+    assert r._uptime(now + timedelta(minutes=5)) is None  # clock skew: not "-5m"
+    assert r._uptime(now - timedelta(days=3, hours=4, seconds=30)) == "3d 4h"