Add Windows compatibility + Minor Refactor

[HungKNguyen]

This pull request adds Windows compatibility to the MCP server, which includes these tasks:

• Modify pnpm scripts to also beable to run on Windows, which involve using the package shx to wrap around Unix commands
• Adding the file pnpm-workspace.yaml to explicitly includes the supported OS and Architectures
• Updating src/fs/sandbox to be Windows compatible (Windows use backslash for path separators compared to Unix's forward slash)
• Update the tests/unit.test.ts so that AI-provided file paths can be OS-agnostic, but the resolved file paths and error message must adhere to the OS standard
• Update README.md

This pull request also refactored the parameter relativeOutputPath to outputFilePath since the output path ultimately get resolved via resolveFilePath which support both relative path and absolute path.

Testing:

• Build and ran the project on Windows 11 64-bit ARM (virtualized)
• Pass all the tests in unit.test.ts
• Connect to the MCP server on Windows using MCP Inspector Tool
• Ran the tests in buid-api-examples.test.ts and signing-api-examples.test.ts
• Test end-to-end on Claude Desktop (Window 11 64-bit ARM virtualized)

Discussion:

• I had to modify the unit.test.ts since the expected result for some test cases changes depending on the OS you are in. For example, the resolved file path can be /sandbox/test.pdf on macOS and C:\sandbox\test.pdf
• While I have not explicitly tested on these platforms, but I think the code should already work on Linux and x64 CPU

[nickwinder]

LGTM .
Just please revert the version prior to merging. Thanks