added --version flag to cli

src/zona/cli.py

@@ -1,3 +1,4 @@
+from importlib.metadata import version as __version__
 from pathlib import Path
 from typing import Annotated
 
@@ -134,8 +135,23 @@ def serve(
     )
 
 
+def version_callback(value: bool):
+    if value:
+        print(f"Zona version: {__version__('zona')}")
+        raise typer.Exit()
+
+
 @app.callback()
 def main_entry(
+    version: Annotated[  # pyright: ignore[reportUnusedParameter]
+        bool | None,
+        typer.Option(
+            "--version",
+            callback=version_callback,
+            is_eager=True,
+            help="Print version info and exit.",
+        ),
+    ] = None,
     verbosity: Annotated[
         str,
         typer.Option(