Rename main to __main__

Most commonly, the __main__.py file is used to provide a command-line
interface for a package. __main__.py will be executed when the package
itself is invoked directly from the command line using the -m flag.

.vscode/launch.json

@@ -6,8 +6,8 @@
             "type": "debugpy",
             "request": "launch",
             "cwd": "${workspaceFolder}",
-            "module": "contact.main",
+            "module": "contact.__main__",
             "args": []
         }
     ]
-}
+}

pyproject.toml

@@ -21,4 +21,4 @@ requires = ["poetry-core>=2.0.0,<3.0.0"]
 build-backend = "poetry.core.masonry.api"
 
 [tool.poetry.scripts]
-contact = "contact.main:start"
+contact = "contact.__main__:start"