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/settings/routes.py

@@ -2,6 +2,7 @@
 from __future__ import annotations
 import html
 import logging
+from datetime import datetime
 from pathlib import Path
 from quart import Blueprint, current_app, render_template, request, redirect, url_for, session
 
@@ -140,6 +141,8 @@ _THRESHOLD_FIELDS = [
     ("tls_warn", "thresholds.tls_warn_days", False), ("tls_crit", "thresholds.tls_crit_days", False),
     ("clock_warn", "thresholds.clock_warn_s", False), ("clock_crit", "thresholds.clock_crit_s", False),
     ("crash_loop_deaths", "thresholds.crash_loop_deaths", False),
+    ("error_5xx_pct", "traefik.threshold.error_5xx_pct", True),
+    ("error_4xx_pct", "traefik.threshold.error_4xx_pct", True),
 ]
 
 # Docker time-series retention windows (days). Read fresh by the cleanup task,
@@ -159,7 +162,9 @@ _RETENTION_FIELDS = [
 async def thresholds():
     async with current_app.db_sessionmaker() as db:
         settings = await get_all_settings(db)
-    return await render_template("settings/thresholds.html", settings=settings)
+    from steward.core.plugin_manager import _LOADED_PLUGINS
+    return await render_template("settings/thresholds.html", settings=settings,
+                                 traefik_on="traefik" in _LOADED_PLUGINS)
 
 
 @settings_bp.post("/thresholds/")
@@ -568,17 +573,36 @@ async def save_auth_settings():
 
 # ── Reports ───────────────────────────────────────────────────────────────────
 
+async def _reports_page(settings: dict, flash):
+    """Settings → Reports, with the schedule and the last send in the reader's
+    zone: the hour is kept in the zone of whoever saved it (#5378)."""
+    from steward.core.formatting import zone
+    from steward.core.reports import schedule_in
+    shown_day, shown_hour = schedule_in(
+        int(settings.get("reports.schedule_day", 6)), int(settings.get("reports.schedule_hour", 8)),
+        zone(settings.get("reports.schedule_tz")), zone(session.get("tz")))
+    raw = settings.get("reports.last_sent_at") or ""
+    try:
+        last_sent = datetime.fromisoformat(raw) if raw else None
+    except ValueError:
+        last_sent = None
+    return await render_template("settings/reports.html", settings=settings, flash=flash,
+                                 shown_day=shown_day, shown_hour=shown_hour, last_sent=last_sent)
+
+
 @settings_bp.get("/reports/")
 @require_role(UserRole.admin)
 async def reports():
     async with current_app.db_sessionmaker() as db:
         settings = await get_all_settings(db)
-    return await render_template("settings/reports.html", settings=settings, flash=None)
+    return await _reports_page(settings, None)
 
 
 @settings_bp.post("/reports/")
 @require_role(UserRole.admin)
 async def save_reports():
+    """The day and hour are what the reader picked on their own clock, so the
+    schedule is kept in their zone."""
     form = await request.form
     async with current_app.db_sessionmaker() as db:
         async with db.begin():
@@ -587,6 +611,7 @@ async def save_reports():
                               int(form.get("reports.schedule_day", 6)))
             await set_setting(db, "reports.schedule_hour",
                               int(form.get("reports.schedule_hour", 8)))
+            await set_setting(db, "reports.schedule_tz", session.get("tz") or "")
     return redirect(url_for("settings.reports"))
 
 
@@ -597,11 +622,7 @@ async def send_report_now():
     async with current_app.db_sessionmaker() as db:
         settings = await get_all_settings(db)
     ok, message = await send_report(current_app._get_current_object())
-    return await render_template(
-        "settings/reports.html",
-        settings=settings,
-        flash={"ok": ok, "message": message},
-    )
+    return await _reports_page(settings, {"ok": ok, "message": message})
 
 
 def _build_plugin_cfg_from_form(plugin: dict, form) -> dict:
@@ -612,9 +633,7 @@ def _build_plugin_cfg_from_form(plugin: dict, form) -> dict:
     for cfg_key in plugin.get("config", {}).keys():
         field_name = f"plugin.{name}.{cfg_key}"
         default_val = plugin["config"][cfg_key]
-        if isinstance(default_val, list):
-            pass  # list configs must be set in plugin.yaml
-        elif isinstance(default_val, dict):
+        if isinstance(default_val, dict):
             sub_dict = {}
             for sub_key, sub_default in default_val.items():
                 sub_field = f"plugin.{name}.{cfg_key}.{sub_key}"