chore(deps): update auth middleware and dependencies

- Add OptionalSessionMiddleware for non-required auth checks
- Add GetUserID helper function
- Update import paths in auth and main
- Update docker-compose with frontend build configuration
- Clean up go.mod and go.sum

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

internal/auth/middleware.go

@@ -5,7 +5,7 @@ import (
 	"net/http"
 	"strings"
 
-	"github.com/writekitapp/writekit/internal/db"
+	"writekit/internal/db"
 )
 
 type ctxKey string
@@ -40,6 +40,21 @@ func GetUserID(r *http.Request) string {
 	return ""
 }
 
+func OptionalSessionMiddleware(database *db.DB) func(http.Handler) http.Handler {
+	return func(next http.Handler) http.Handler {
+		return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+			token := extractToken(r)
+			if token != "" {
+				if session, err := database.ValidateSession(r.Context(), token); err == nil && session != nil {
+					ctx := context.WithValue(r.Context(), userIDKey, session.UserID)
+					r = r.WithContext(ctx)
+				}
+			}
+			next.ServeHTTP(w, r)
+		})
+	}
+}
+
 func extractToken(r *http.Request) string {
 	if cookie, err := r.Cookie("writekit_session"); err == nil && cookie.Value != "" {
 		return cookie.Value