Rename readme.md to README.md to fix error

[c0d33ngr]

This PR will fix the error below which has an open issue at #211.

 × Failed to build `ce3 @ file:///workspaces/claude-engineer`
  ├─▶ The build backend returned an error
  ╰─▶ Call to `hatchling.build.build_editable` failed (exit status: 1)

      [stderr]
      Traceback (most recent call last):
        File "<string>", line 11, in <module>
        File "/home/codespace/.cache/uv/builds-v0/.tmpI9qLnn/lib/python3.12/site-packages/hatchling/build.py", line 83, in build_editable
          return os.path.basename(next(builder.build(directory=wheel_directory, versions=['editable'])))
                                  ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
        File "/home/codespace/.cache/uv/builds-v0/.tmpI9qLnn/lib/python3.12/site-packages/hatchling/builders/plugin/interface.py", line 90,
      in build
          self.metadata.validate_fields()
        File "/home/codespace/.cache/uv/builds-v0/.tmpI9qLnn/lib/python3.12/site-packages/hatchling/metadata/core.py", line 266, in
      validate_fields
          self.core.validate_fields()
        File "/home/codespace/.cache/uv/builds-v0/.tmpI9qLnn/lib/python3.12/site-packages/hatchling/metadata/core.py", line 1366, in
      validate_fields
          getattr(self, attribute)
        File "/home/codespace/.cache/uv/builds-v0/.tmpI9qLnn/lib/python3.12/site-packages/hatchling/metadata/core.py", line 531, in readme
          raise OSError(message)
      OSError: Readme file does not exist: README.md

      hint: This usually indicates a problem with the package or the build environment.