fix: make the env var of the child shell consistent with parent shell (#202)

Closes #185

* fix: make the env var of the child shell consistent with parent shell

* [pre-commit.ci] auto fixes from pre-commit.com hooks

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---------

Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>

Author: aoyanli

src/swerex/runtime/local.py

@@ -1,4 +1,5 @@
 import logging
+import os
 import re
 import shutil
 import subprocess
@@ -159,7 +160,7 @@ async def start(self) -> CreateBashSessionResponse:
             encoding="utf-8",
             codec_errors="backslashreplace",
             echo=False,
-            env={"PS1": self._ps1, "PS2": "", "PS0": ""},  # type: ignore
+            env=dict(os.environ.copy(), **{"PS1": self._ps1, "PS2": "", "PS0": ""}),  # type: ignore
         )
         time.sleep(0.3)
         cmds = []