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/models/registry.go

@@ -1,5 +1,7 @@
 package models
 
+import "strings"
+
 type ModelRegistry struct {
 	Providers map[string]ProviderInfo `json:"-"`
 }
@@ -54,5 +56,14 @@ func (r *ModelRegistry) FindModel(modelID string) *ModelMetadata {
 		}
 	}
 
+	// Try fuzzy matching (e.g. gpt-4o-2024-05-13 matching gpt-4o)
+	for _, provider := range r.Providers {
+		for id, model := range provider.Models {
+			if strings.HasPrefix(modelID, id) {
+				return &model
+			}
+		}
+	}
+
 	return nil
 }