feat(hosts): one health header, graded by one set of thresholds (#5122)

The host page's vitals strip becomes its health header: Live or Stale,
then one sentence — "Memory 93% is past its critical threshold", "Every
reading is within its thresholds", or, for a stale host, "No report since
20m ago; the readings below are from then" — and last seen as |ago. CPU,
memory, root disk and load per core follow as stat tiles graded by
Settings → Thresholds, with their sparklines.

The full-metrics page drew its bars and gauges at a hard-coded 70/90
(temperatures 70/85) while every other page used the configured cutoffs
(80/90 by default), so a 75 % CPU was amber here and fine everywhere else.
bar() now takes the metric kind and colours its .meter-fill through
status_class; gauges, temperatures and per-core bars do the same.

The host's monitor rows move onto the Monitors list's shapes: a status dot,
the name linking to the monitor's page, Ping/TCP/DNS/HTTP, pill-up/
pill-down, latency and uptime through status_class, labelled icon buttons.
HEX_CEILING drops to 54.

New formatting.worst_reading(readings, thresholds) picks the reading
furthest past its cutoff, the first of equals winning.

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

tests/test_style_tokens.py

@@ -22,7 +22,7 @@ _USED = re.compile(r"var\(\s*(--[\w-]+)")
 # string -- but not an HTML attribute's value (href="#abc" is a link to an id).
 _HEX = re.compile(r"""(?:[:(,]\s*|(?<![\w-]=)['"])#(?:[0-9a-fA-F]{8}|[0-9a-fA-F]{6}|[0-9a-fA-F]{3})(?![0-9a-zA-Z_-])""")
 
-HEX_CEILING = 56  # 75 at #5092, 58 at #5095, 56 with the Monitors list on tokens (#5121); only lower it
+HEX_CEILING = 54  # 75 at #5092, 58 at #5095, 56 at #5121, 54 with the host page on tokens (#5122); only lower it
 
 
 def _sheets():