feat(settings): Settings brought into line with the rest of Steward (milestone 493)

The last page of #5214's walk. Settings still described Steward as it was
before monitors were unified and SNMP was rebuilt, drew its tabs below the
breadcrumb, and showed the report schedule in UTC.

- Tabs (#5377): settings/_tabs.html is a settings_tabs() macro called in
  each page's section_tabs block, above the trail, as Ansible's are. The
  breadcrumb guard also fails any page that {% include %}s a tab strip.
- Report time (#5378): reports.schedule_tz keeps the zone of whoever saved
  the schedule; check_and_send compares in it (report_due), and the form shows
  the day and hour on the reader's clock (schedule_in) under their zone's
  name. "Last sent" uses |when.
- Wording (#5379): the report contents list what the report holds (monitors,
  not ping-enabled hosts); "Ping latency" is "Response time" and says what it
  grades; plugin detail says enabling loads now and disabling needs a
  restart; the monitor interval says it applies on the next check (the
  scheduler reads it every pass); the dead list-config branch is gone.
- Traefik (#5380): the 5xx and 4xx cutoffs are settings
  (traefik.threshold.error_5xx_pct 0.1, error_4xx_pct 1.0) in a "Traefik
  routers" group on Thresholds while the plugin runs, read by router_state
  through error_cutoffs(). The Traefik page has a Thresholds button for
  admins, to /settings/thresholds/#traefik.

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

steward/templates/settings/_tabs.html

@@ -1,20 +1,13 @@
-{# settings/_tabs.html — include at top of each settings section.
-   No section <h1>: the breadcrumb kicker ("Settings › …") names the section and
-   the tab strip is the visual header, so we don't stack a redundant title. #}
-<div style="display:flex;gap:0;border-bottom:1px solid var(--border-mid);margin-bottom:1.5rem;">
-  {% set tabs = [
-    ("general",       "General",        "/settings/general/"),
-    ("thresholds",    "Thresholds & Retention", "/settings/thresholds/"),
-    ("notifications", "Notifications",  "/settings/notifications/"),
-    ("reports",       "Reports",        "/settings/reports/"),
-    ("auth",          "Authentication", "/settings/auth/"),
-    ("ansible",       "Ansible",        "/settings/ansible/"),
-    ("plugins",       "Plugins",        "/settings/plugins/"),
-  ] %}
-  {% for key, label, href in tabs %}
-  <a href="{{ href }}"
-     style="padding:0.6rem 1.1rem;font-size:0.875rem;border-bottom:2px solid {{ 'var(--accent)' if active_tab == key else 'transparent' }};color:{{ 'var(--text)' if active_tab == key else 'var(--text-muted)' }};font-weight:{{ '500' if active_tab == key else 'normal' }};text-decoration:none;">
-    {{ label }}
-  </a>
-  {% endfor %}
-</div>
+{# settings/_tabs.html — the Settings section's pages as one strip of tabs, in
+   each page's section_tabs block above the trail, as Ansible's are (#5377).
+   `active` names the page or the one it sits under. #}
+{% from "_macros.html" import section_tabs %}
+{% macro settings_tabs(active) -%}
+{{ section_tabs([("general", "General", "/settings/general/"),
+                 ("thresholds", "Thresholds & Retention", "/settings/thresholds/"),
+                 ("notifications", "Notifications", "/settings/notifications/"),
+                 ("reports", "Reports", "/settings/reports/"),
+                 ("auth", "Authentication", "/settings/auth/"),
+                 ("ansible", "Ansible", "/settings/ansible/"),
+                 ("plugins", "Plugins", "/settings/plugins/")], active, "Settings") }}
+{%- endmacro %}