fixed crash on missing templates dir when starting server

src/zona/server.py

@@ -237,11 +237,13 @@ def serve(
         observer.schedule(
             event_handler, path=str(root / "content"), recursive=True
         )
-        observer.schedule(
-            event_handler,
-            path=str(root / "templates"),
-            recursive=True,
-        )
+        templates = root / "templates"
+        if templates.is_dir():
+            observer.schedule(
+                event_handler,
+                path=str(templates),
+                recursive=True,
+            )
         observer.start()
 
         # function to shut down gracefully