feat(ui): base stylesheet on the Steward design-system tokens; readable status colours (#5092)

#5092 "Tokens". base.html's inline palette was its own: white text on the
gold button (1.81:1), a red at 3.26:1 on a card, a warning yellow at hue
42 beside the gold accent at 46, a lavender page title, serif labels at
13px and weights up to 700.

- static/theme.css is design system 6's generated sheet (FabledSword + the
  Steward accent). static/steward.css is base.html's stylesheet moved out,
  with :root now aliases onto those tokens (--bg, --text-muted, --green…)
  so every template keeps rendering; it states no colour of its own.
- Status text colours are Steward overrides recorded in the design system
  (tokens 182-184): success #5FB87A, warning #E08A3C, error #EC7A6C. The
  house -fg mixes read "up" as grey hint text (dE 8.2) and warning as the
  accent (dE 11.5); these are >= 4.5:1 on page, card, hover and their own
  15-25% tints. --orange is now the midpoint of warning and error.
- Primary button and active range button: dark text on gold (7.82:1).
  Danger button on the house destructive fill. Badges and alerts take the
  -fg colour on a tint; the gold badge uses --fs-accent-fg.
- Type: Inter body, Fraunces only for page titles and h1/h2, JetBrains
  Mono for code; section and widget titles become the tiny caps label in
  the body face; weights capped at 500.
- Removed: the lavender title and share-view gradient, #606080, and the
  undefined --card-bg, --accent-faint, --accent-bg, --bg-alt, --border-low
  and --row-alt (now real tokens); the dead settings/index.html.
- Guards (tests/test_style_tokens.py): every var(--x) used is defined;
  steward.css states no colour or weight over 500; hex colours in
  templates may only go down (ceiling 75, from 81 before this change),
  each with a self-test that it can fail.

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

plugins/host_agent/templates/settings_list.html

@@ -12,7 +12,7 @@
 </p>
 
 {% if new_token %}
-<div class="card" style="background:var(--accent-bg);">
+<div class="card" style="background:var(--fs-accent-faint);">
   <h3>New token — copy this install command now</h3>
   <p style="font-size:0.82rem;color:var(--text-muted);">
     This is the only time the raw token is shown. Rotate if you lose it.