refactor: move Claims type from auth to new identity package

Extract Claims struct from auth/types.go into dedicated identity package for better separation of concerns. Update all imports and usages across auth service, token handling, and request context utilities.

backend/internal/requestctx/context.go

@@ -5,19 +5,19 @@ import (
 
 	"github.com/google/uuid"
 
-	"github.com/nexavpn/nexavpn/backend/internal/auth"
+	"github.com/nexavpn/nexavpn/backend/internal/identity"
 )
 
 type contextKey string
 
 const claimsKey contextKey = "claims"
 
-func WithClaims(ctx context.Context, claims auth.Claims) context.Context {
+func WithClaims(ctx context.Context, claims identity.Claims) context.Context {
 	return context.WithValue(ctx, claimsKey, claims)
 }
 
-func ClaimsFromContext(ctx context.Context) (auth.Claims, bool) {
-	claims, ok := ctx.Value(claimsKey).(auth.Claims)
+func ClaimsFromContext(ctx context.Context) (identity.Claims, bool) {
+	claims, ok := ctx.Value(claimsKey).(identity.Claims)
 	return claims, ok
 }