chore: consolidate env files and update gitignore

Removed .env and .env.backup from git tracking and consolidated configuration into .env.example. Updated .gitignore to robustly prevent accidental inclusion of sensitive files.

internal/utils/registry.go

@@ -0,0 +1,54 @@
+package utils
+
+import (
+	"encoding/json"
+	"fmt"
+	"log"
+	"time"
+
+	"llm-proxy/internal/models"
+	"github.com/go-resty/resty/v2"
+)
+
+const ModelsDevURL = "https://models.dev/api.json"
+
+func FetchRegistry() (*models.ModelRegistry, error) {
+	log.Printf("Fetching model registry from %s", ModelsDevURL)
+
+	client := resty.New().SetTimeout(10 * time.Second)
+	resp, err := client.R().Get(ModelsDevURL)
+	if err != nil {
+		return nil, fmt.Errorf("failed to fetch registry: %w", err)
+	}
+
+	if !resp.IsSuccess() {
+		return nil, fmt.Errorf("failed to fetch registry: HTTP %d", resp.StatusCode())
+	}
+
+	var providers map[string]models.ProviderInfo
+	if err := json.Unmarshal(resp.Body(), &providers); err != nil {
+		return nil, fmt.Errorf("failed to unmarshal registry: %w", err)
+	}
+
+	log.Println("Successfully loaded model registry")
+	return &models.ModelRegistry{Providers: providers}, nil
+}
+
+func CalculateCost(registry *models.ModelRegistry, modelID string, promptTokens, completionTokens, cacheRead, cacheWrite uint32) float64 {
+	meta := registry.FindModel(modelID)
+	if meta == nil || meta.Cost == nil {
+		return 0.0
+	}
+
+	cost := (float64(promptTokens) * meta.Cost.Input / 1000000.0) +
+		(float64(completionTokens) * meta.Cost.Output / 1000000.0)
+
+	if meta.Cost.CacheRead != nil {
+		cost += float64(cacheRead) * (*meta.Cost.CacheRead) / 1000000.0
+	}
+	if meta.Cost.CacheWrite != nil {
+		cost += float64(cacheWrite) * (*meta.Cost.CacheWrite) / 1000000.0
+	}
+
+	return cost
+}