feat: add PowerShell install script for flex-ax camp on Windows

[longfin]

Summary

• Add scripts/install-common.ps1 — PowerShell port of shared install functions (Install-FlexAx, Install-Gws, Install-GwsAuth, Install-CampFiles, Detect-Platform, Generate-Adapters, and all platform adapters)
• Add camps/flex-ax/install.ps1 — PowerShell port of the flex-ax camp installer with identical workflow to install.sh
• Uses .cmd wrappers instead of Unix symlinks, Invoke-WebRequest for downloads, and Windows-appropriate paths ($env:APPDATA, ; PATH separator)

Fixes #32

Test plan

• Run install.ps1 on a Windows machine with Node.js/npm installed
• Verify Install-FlexAx creates .local/bin/flex-ax.cmd wrapper
• Verify Install-Gws creates .local/bin/gws.cmd wrapper
• Verify Install-GwsAuth creates .local/bin/gws-auth.cmd wrapper
• Verify Install-CampFiles extracts identity/knowledge/scripts correctly
• Verify Generate-Adapters creates .claude/CLAUDE.md with @ references
• Verify freshness check hook is written to .claude/settings.json

🤖 Generated with Claude Code

[longfin]

Reviewed locally on Windows. I found two blocking issues in the PowerShell installer path.

1. Install-GwsAuth is looking for the installed CLI entrypoint under @anthropic-kr/gws-auth, but the tarball actually installs under @planetarium/gws-auth. I reproduced this by running the install locally: after npm install --prefix $prefix $url, the file on disk was .local/node_modules/@planetarium/gws-auth/bin/gws-auth.js, so the current Test-Path $cliJs check fails and no gws-auth.cmd wrapper is created.

2. The documented remote install.ps1 flow appears broken in the fallback branch. When users run irm .../install.ps1 | iex, $MyInvocation.MyCommand.Path is not a real on-disk script path, so this code falls back to downloading install-common.ps1 from the release. But the current flex-ax-v1.1.0 release only contains install-common.sh, not install-common.ps1, so the fallback cannot succeed for the primary remote-install scenario.

Because both of these affect the actual Windows install path, I don’t think this one is ready yet.

[longfin]

Fixed both issues: gws-auth package scope corrected to @planetarium/gws-auth, and remote install fallback now fetches install-common.ps1 from raw.githubusercontent.com.