feat: Add Windows compatibility guide and installer support

[chrisglick]

Summary

• Windows Compatibility Guide (Releases/v3.0/WINDOWS_COMPATIBILITY.md) — comprehensive manual installation steps, known issues, and workarounds for running PAI on Windows
• Installer Windows detection — install.sh now detects MINGW/MSYS/CYGWIN and directs users to the compatibility guide instead of failing with "Unsupported platform"
• Install-time hook path resolution — resolveHookPaths() in actions.ts resolves ${PAI_DIR} in hook commands on Windows only (complete no-op on macOS/Linux), since cmd.exe doesn't expand ${VAR} syntax

Problem

Claude Code hooks on Windows fail with Module not found "${PAI_DIR}/hooks/..." because:

1. ${PAI_DIR} in hook command strings is expanded by /bin/sh on macOS/Linux, but Windows hooks execute through cmd.exe which uses %VAR% syntax
2. .ts hook files have #!/usr/bin/env bun shebangs that work on Unix but not Windows — they need explicit bun prefixing

Changes

File	Change
Releases/v3.0/WINDOWS_COMPATIBILITY.md	New: manual install guide, known issues, workarounds
Releases/v3.0/.claude/PAI-Install/engine/actions.ts	Added resolveHookPaths() — Windows-only, no-op on macOS/Linux
Releases/v3.0/.claude/PAI-Install/install.sh	Added MINGW/MSYS/CYGWIN detection with helpful error message
README.md	Added one-line Windows reference pointing to guide
Releases/v3.0/README.md	Added one-line Windows reference pointing to guide

Design Decisions

• Zero Mac/Linux impact: resolveHookPaths() returns immediately on non-win32 platforms. No behavioral changes for existing users.
• Template stays generic: The template settings.json still uses ${PAI_DIR} — resolution happens at install time only, so the template remains portable.
• Forward slashes on Windows: All resolved paths use / separators since both Bun and Node.js handle them correctly on Windows.

Test plan

• Verify install.sh on macOS/Linux still works unchanged
• Verify install.sh on Windows (Git Bash/MSYS) shows compatibility guide message
• Run TypeScript installer on Windows — confirm hooks resolve correctly
• Confirm resolveHookPaths() is a no-op when process.platform !== "win32"

Closes #440, #543, #385

🤖 Generated with Claude Code

[chrisglick]

Research Note: Why Install-Time Resolution Is Correct

While reviewing this PR, I investigated whether we could use %PAI_DIR% (cmd.exe runtime expansion) instead of hardcoding absolute paths at install time — preserving the same flexibility that ${PAI_DIR} provides on macOS/Linux.

Finding: It won't work. There's a known Claude Code bug:

• #20112 (duplicate of #11927): Environment variables from settings.json's env section are not injected into hook command execution on Windows. The PAI_DIR value defined in env never reaches the shell that runs hook commands.

Even if the bug were fixed, there's a shell ambiguity problem:

• %PAI_DIR% only works in cmd.exe
• PowerShell needs $env:PAI_DIR
• Bash/MSYS needs ${PAI_DIR}
• Claude Code's official Windows hook examples use powershell.exe -Command "..." explicitly, but don't guarantee which shell runs hook commands

Conclusion: resolveHookPaths() doing install-time absolute path resolution is the correct approach for Windows. It sidesteps both the env var injection bug and the shell syntax ambiguity. When #11927 is fixed, this could potentially be simplified to a syntax swap (${PAI_DIR} → %PAI_DIR%) rather than full path resolution — but that's a future optimization.