fix(traefik): grade routers on their last 15 minutes; the Config tile reads Traefik's reload time (#5355)

The operator: problem cards "can disappear so quickly". Each router was
graded on its latest scrape, so a 4xx share near the 1% cutoff crossed it
on one scrape and fell back on the next. recent_window reads every
router's last 15 minutes in one query, the error shares weighted by
traffic; grade_routers uses it on the page and the dashboard widget, and
the why says "over the last 15 min".

traefik_config_last_reload_success is the Unix time of the last good
reload, not a 0/1 flag, so the tile said "Reload failed" on every scrape.
traefik_005 stores it as config_last_reload_at, and the tile reads
"Config reloaded 3m ago". The router index also carries the 4xx share.

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

plugins/traefik/templates/traefik/rows.html

@@ -8,9 +8,8 @@
   {{ stat_tile("Needs attention", problems|length, state="crit" if problems else "inactive") }}
   {{ stat_tile("Healthy routers", healthy|length, state="up" if healthy else "inactive") }}
   {% if global_stat %}
-  {% if global_stat.config_last_reload_success is not none %}
-  {{ stat_tile("Config", "OK" if global_stat.config_last_reload_success == 1.0 else "Reload failed",
-               state="up" if global_stat.config_last_reload_success == 1.0 else "crit",
+  {% if global_stat.config_last_reload_at %}
+  {{ stat_tile("Config reloaded", global_stat.config_last_reload_at|ago,
                hint=(global_stat.config_reloads_total|int ~ " reloads") if global_stat.config_reloads_total is not none else none) }}
   {% endif %}
   {% if global_stat.open_conns_total is not none %}{{ stat_tile("Open connections", global_stat.open_conns_total|int) }}{% endif %}