feat: add Windows PowerShell installation and conversion scripts

[ALVIN-YANG]

Summary

Added scripts/install.ps1 and scripts/convert.ps1 to natively support Windows users, replicating the behavior of the existing bash scripts. Also updated README.md to reference the new PowerShell scripts.

Resolves #153.

Problem statement

The project provides install.sh and convert.sh which only run natively on Mac/Linux (or require Git Bash/WSL on Windows). Many Windows users expect native PowerShell script equivalents (.ps1) to avoid installing additional environment tooling.

Proposed solution

1. Created scripts/install.ps1 to mimic install.sh with interactive tool selection and auto-detection, correctly routing integration directories to $env:USERPROFILE.
2. Created scripts/convert.ps1 to mimic convert.sh, capable of reading markdown frontmatter and extracting body blocks to build all the integration variants exactly as the bash script does.
3. Updated README.md usage section to clarify the commands for Windows users.

Acceptance criteria

Windows users can run .\scripts\install.ps1 and .\scripts\convert.ps1 seamlessly.

[msitarzewski]

Hey @ALVIN-YANG — thanks for this. Clean implementation.

Heads up: PR #171 from @RoyCoding8 covers the same ground (PowerShell convert + install scripts) with some extras (CMD wrappers, lint support). We can't merge both.

Rather than picking one, would you be open to collaborating with @RoyCoding8 on a single combined PR? Your compact implementation style + their CMD wrappers and lint support could make a strong joint effort.

See the comment on #171 for more context.

[msitarzewski]

Heads up: we're consolidating the Windows support conversation into a single Discussion: #197 — please weigh in there so we can align on one approach.