feat(ui): the continuous complexity score shows next to the tier

Benchmark (routing mode) and the dashboard's recent-requests list now print
the router's raw 0..1 score under/next to the tier badge — people can see
what different prompts actually weigh and tune the boundary sliders from
real data. Tooltip explains the link to the Routing sliders (7 languages).

Caught before commit: naming the field row.score collided with the answer-
correctness fraction from evaluate() and dragged the benchmark's quality KPI
down to the average complexity — renamed to cscore, KPI verified back at
100%. Dashboard tier badges also render translated names now, and the
Russian locale calls the dashboard «Рабочий стол».

web/js/i18n/en.js

@@ -627,4 +627,5 @@ export default {
   "tier.low": "low",
   "tier.medium": "medium",
   "tier.high": "high",
+  "bm.scoreHint": "The router's continuous complexity score (0..1) — the boundary sliders on the Routing page cut it into tiers.",
 };