feat(ui): share view on steward.css; breadcrumbs everywhere they belong; focus ring; tables scroll in their card (#5095)

#5095 "Share view on the shared stylesheet; breadcrumbs, focus-visible and
wide tables".

- dashboard/share_view.html loads theme.css and steward.css; its own copy of
  the old purple palette is gone. Only the read-only frame and the x/y/w/h
  grid stay inline, written in tokens. HEX_CEILING 75 -> 58.
- Breadcrumbs on settings/general, settings/thresholds, the dashboard share
  page and share-link-created. tests/test_breadcrumbs.py fails on any page
  extending base.html without a crumbs() trail, unless it is on the named
  list of section top pages, logged-out and error pages (rule 134).
- :focus-visible draws --fs-focus-ring on links, buttons, summaries, inputs
  and anything with tabindex.
- Any card holding a .table scrolls sideways (card:has(table.table)), so a
  wide table no longer widens the page at phone width; .card-flush scrolls
  too, main gets min-width:0, and .table-wrap covers a table outside a card.
- tests/test_share_view.py renders the share view: shared sheets, no hex
  colour, escaped name, widgets loading through the share token.

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

steward/templates/settings/thresholds.html

@@ -1,6 +1,8 @@
 {# steward/templates/settings/thresholds.html — tunable degraded/critical cutoffs #}
 {% extends "base.html" %}
+{% from "_macros.html" import crumbs %}
 {% block title %}Settings — Thresholds & Retention — Steward{% endblock %}
+{% block breadcrumb %}{{ crumbs([("Settings", "/settings/"), ("Thresholds & retention", "")]) }}{% endblock %}
 {% block content %}
 {% set active_tab = "thresholds" %}
 {% include "settings/_tabs.html" %}