feat(usage): track cached tokens + correct input/output/cache cost (#2209)

Normalize every provider to one cache-inclusive convention via
canonicalizeUsage() before persist, and price cached + cache_creation as
subsets of prompt_tokens in calculateCostFromTokens() to stop
double-counting. usageRepo now delegates cost math to a single source.
Surface Cached tokens/cost across dashboard (overview, tokens, cost,
details). Merge Claude message_start cache with message_delta output so
cache counts survive. Compatible LLM nodes now allow multiple API-key
connections (key pool).

Co-authored-by: Cursor <cursoragent@cursor.com>

src/app/(dashboard)/dashboard/usage/components/OverviewCards.js

@@ -8,7 +8,7 @@ const fmtCost = (n) => `$${(n || 0).toFixed(2)}`;
 
 export default function OverviewCards({ stats }) {
   return (
-    <div className="grid min-w-0 grid-cols-1 gap-3 sm:grid-cols-2 md:grid-cols-4 sm:gap-4">
+    <div className="grid min-w-0 grid-cols-1 gap-3 sm:grid-cols-2 md:grid-cols-3 lg:grid-cols-5 sm:gap-4">
       <Card className="flex min-w-0 flex-col gap-1 px-4 py-3">
         <span className="text-text-muted text-sm uppercase font-semibold">Total Requests</span>
         <span className="truncate text-2xl font-bold">{fmt(stats.totalRequests)}</span>
@@ -17,6 +17,10 @@ export default function OverviewCards({ stats }) {
         <span className="text-text-muted text-sm uppercase font-semibold">Total Input Tokens</span>
         <span className="truncate text-2xl font-bold text-primary">{fmt(stats.totalPromptTokens)}</span>
       </Card>
+      <Card className="flex min-w-0 flex-col gap-1 px-4 py-3">
+        <span className="text-text-muted text-sm uppercase font-semibold">Cached Tokens</span>
+        <span className="truncate text-2xl font-bold text-info">{fmt(stats.totalCachedTokens)}</span>
+      </Card>
       <Card className="flex min-w-0 flex-col gap-1 px-4 py-3">
         <span className="text-text-muted text-sm uppercase font-semibold">Output Tokens</span>
         <span className="truncate text-2xl font-bold text-success">{fmt(stats.totalCompletionTokens)}</span>