Fix #117: include .md prompt files in wheel + handle Windows temp-dir cleanup

Fix 1: Add [tool.setuptools.package-data] to pyproject.toml so that
all .md prompt files (generic prompts under skillopt/prompts/ and
env-specific prompts under skillopt/envs/*/prompts/) are included
in the wheel. Previously pip install from PyPI would fail with
FileNotFoundError on first prompt load.

Fix 2: Replace TemporaryDirectory context manager with mkdtemp +
shutil.rmtree(ignore_errors=True) in claude_backend._run_claude_print.
On Windows, the spawned claude/node subprocess still holds a handle
on the temp directory when the context manager tries to clean up,
causing WinError 32. Manual rmtree with ignore_errors=True works
on all Python versions >= 3.10.

Co-Authored-By: Claude <noreply@anthropic.com>

pyproject.toml

@@ -73,6 +73,9 @@ Issues = "https://github.com/microsoft/SkillOpt/issues"
 # skillopt_webui = the Gradio dashboard (installed via the `webui` extra)
 include = ["skillopt", "skillopt.*", "skillopt_sleep", "skillopt_sleep.*", "skillopt_webui", "skillopt_webui.*", "scripts*"]
 
+[tool.setuptools.package-data]
+"*" = ["*.md"]
+
 [tool.ruff]
 line-length = 120
 target-version = "py310"