fix: improve analytics accuracy and cost calculation

Refined CalculateCost to correctly handle cached token discounts. Added fuzzy matching to model lookup. Robustified SQL date extraction using SUBSTR and LIKE for better SQLite compatibility.

internal/utils/registry.go

@@ -40,7 +40,18 @@ func CalculateCost(registry *models.ModelRegistry, modelID string, promptTokens,
 		return 0.0
 	}
 
-	cost := (float64(promptTokens) * meta.Cost.Input / 1000000.0) +
+	// promptTokens is usually the TOTAL prompt size.
+	// We subtract cacheRead from it to get the uncached part.
+	uncachedTokens := promptTokens
+	if cacheRead > 0 {
+		if cacheRead > promptTokens {
+			uncachedTokens = 0
+		} else {
+			uncachedTokens = promptTokens - cacheRead
+		}
+	}
+
+	cost := (float64(uncachedTokens) * meta.Cost.Input / 1000000.0) +
 		(float64(completionTokens) * meta.Cost.Output / 1000000.0)
 
 	if meta.Cost.CacheRead != nil {