feat(traefik): routers are graded against their own normal (#5741)

#5741 "Traefik routers are graded against their own normal", milestone 513.

- A router's 4xx share and p95 learn their normal (learn_normal in the
  plugin's setup). Once a router has 5 days of history, a reading over the
  fixed cutoff but inside its normal is healthy, and the healthy table says
  it is usual for that router. One out of its normal is a warning that says
  what is usual, and a metric anomaly.
- The 5xx share is a failure: fixed cutoff always, whatever the history or
  traffic (System 182's ruling).
- A 4xx share over fewer requests than Settings -> Thresholds' new "Fewest
  requests to judge 4xx" (30 per 15 minutes) isn't graded on the page, and
  isn't judged for anomalies.
- Core: learn_normal(gate=(metric, least)) judges a key only while its
  resource's gate metric averages at least `least`; `least` may be a
  function, so it follows a setting. learn_normal(since=...) learns only
  from history after a moment: Traefik latency learns from #5755's
  per-scrape figures only.
- The Traefik page lists the routers' metric anomalies of the last 30 days
  (_anomaly_card.html). The dashboard widget keeps its why to problems.
- Thresholds and docs say when the cutoffs give way to a normal.

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

plugins/traefik/templates/traefik/rows.html

@@ -1,7 +1,8 @@
 {# traefik/rows.html — HTMX fragment for the Traefik page: the verdict (swapped
    into #traefik-verdict above the request chart, #5710), routers that need
-   attention (routes.router_state), the proxy's own figures, the healthy
-   routers folded into one table, then certificates by soonest expiry. #}
+   attention (routes.router_state), their metric anomalies, the proxy's own
+   figures, the healthy routers folded into one table (one over a cutoff but
+   within its normal says so, #5741), then certificates by soonest expiry. #}
 {% from "_macros.html" import stat_tile, status_badge %}
 
 {# ── Verdict: what needs a look and since when, then the counts ─────────── #}
@@ -77,6 +78,10 @@
 </div>
 {% endif %}
 
+{# A router's 4xx share or p95 out of its own normal (#5741), and the last
+   30 days' anomalies, to review here. #}
+{% include "_anomaly_card.html" %}
+
 {{ proxy_figures() }}
 
 {# ── Healthy routers, folded ─────────────────────────────────────────────── #}
@@ -89,7 +94,7 @@
     <tbody>
     {% for r in healthy %}
     <tr>
-      <td style="word-break:break-all;">{{ r.name }}</td>
+      <td style="word-break:break-all;">{{ r.name }}{% if r.why %}<div class="field-hint">{{ r.why }}</div>{% endif %}</td>
       <td>{{ "%.2f"|format(r.latest.request_rate) }}</td>
       <td>{{ r.latest.response_bytes_rate|rate }}</td>
       {{ latency_cell(r.latest.latency_p95_ms) }}

plugins/traefik/templates/traefik/widget.html

@@ -24,7 +24,7 @@
     <td class="w-name" title="{{ r.name }}">
       {{- status_dot(r.state) -}}
       {{ r.name.split('@')[0] }}
-      {%- if r.why %}<span class="w-sub tone-{{ r.state }}">{{ r.why }}</span>{% endif %}
+      {%- if r.why and r.state != "ok" %}<span class="w-sub tone-{{ r.state }}">{{ r.why }}</span>{% endif %}
     </td>
     <td>{% if m.request_rate is none %}—{% else %}{{ "%.2f"|format(m.request_rate) }}{% endif %}</td>
     <td class="w-wide-only">{% if m.response_bytes_rate is none %}—{% else %}{{ m.response_bytes_rate|rate }}{% endif %}</td>