fix(webui): accessible warn token, day-window model badges, review minors

Review round (v0.22) — MUST-1, SHOULD-2's frontend half, and every
folded minor that touched webui/.

MUST-1 (contrast): the degraded badge's amber previously reused
--color-chart-tokens-out, tuned for a chart mark, not body text —
measured ~2.22:1 against --card in light mode, a WCAG 1.4.3 failure on
exactly the "something's wrong" tier. A new semantic --status-warn token
pair (main.css, with a @theme inline mapping) replaces it: #a35c00 light
(~5.06:1), #f0ac1f dark (~8.97:1, already passing, redefined anyway so
every semantic-color token's dark value lives in one place).
ProviderRateBadge.vue's degraded tier now uses border-status-warn/40
text-status-warn.

SHOULD-2 (frontend half — see the backend commit for admin.go/limits.go):
AdminModelRateView drops attemptsMinute/failuresMinute (the backend no
longer sends them at all). ProviderRateBadge.vue's attempts-minute/
failures-minute props become optional; their absence (not a passed-
through 0) triggers a new dayRateTitle fallback (lib/provider-rate.ts) —
a real "0 attempts this minute" and "no minute data fetched at all" read
identically as 0 otherwise, which would misreport a model badge as having
live-minute data it never measured.

Folded minors:
- formatRatePercent floors instead of rounds — only a true 100% rate
  (zero failures) ever renders "100%"; 99.6% now shows "99%", not a
  round-tripped "100%" that would overstate it.
- providerSuccessRate NaN-guards both inputs (Number.isFinite).
- ProvidersView's modelRateFor uses `p.modelRates?.[model]` — a stale
  client against an older server build could otherwise throw rather than
  fall back, matching its own doc comment's stated intent.
- ProviderRateBadge's title is now also its aria-label — title alone is
  mouse-only; a keyboard/screen-reader user previously got none of the
  minute/day detail.
- The accordion's "Last refresh" DETAIL row (not just the trigger's
  compact text) now shares refreshLabel's three-state logic via a new
  refreshDetailLabel (lib/format.ts) — it previously called
  formatTimestamp directly, so a discovery-off provider's expanded row
  still said "never" beside a trigger that correctly said "discovery
  off".
- providerModelScopeID's Go doc comment (limits.go, backend commit)
  cross-references configNamePattern for why the "/" join is collision-
  safe even though a model id may itself contain "/".
- useTabHash.ts documents its two intentional URL-normalization quirks:
  case-sensitive hash matching, and an invalid/absent initial hash
  normalizing only in memory, not in the address bar, until the next tab
  change.

webui/src/composables/useTabHash.ts

@@ -18,6 +18,20 @@ import { onMounted, onUnmounted, ref, watch } from 'vue'
  * validTabs. Matching is a plain string comparison: a tab value is
  * already a fixed lowercase identifier (App.vue's TabsTrigger value=
  * strings), never re-cased anywhere in this pipeline.
+ *
+ * Two intentional URL-normalization quirks (folded review minors, v0.22
+ * review round), both worth naming rather than leaving implicit:
+ *
+ * 1. Case sensitivity: "#Providers" does NOT match "providers" — it falls
+ *    back to defaultTab like any other unrecognized hash, rather than
+ *    being normalized case-insensitively. A URL a person typed or edited
+ *    by hand with different casing is treated as invalid, not corrected.
+ * 2. An invalid or absent hash is normalized only in memory (this
+ *    function's own return value), never in the address bar itself:
+ *    useTabHash's initial read below never calls history.replaceState —
+ *    only a LATER tab change does (see its own doc comment) — so loading
+ *    "#bogus" shows the Providers tab while the address bar still reads
+ *    "#bogus" until the reader switches tabs at least once.
  */
 export function hashToTab<T extends string>(hash: string, validTabs: readonly T[], defaultTab: T): T {
   const raw = hash.startsWith('#') ? hash.slice(1) : hash