feat(windows): native auto-rewrite hook support + install.ps1

[279814]

Summary

Native Windows already runs the auto-rewrite hook today — the Claude Code hook is the platform-agnostic rtk hook claude subcommand, and rtk init -g registers it on Windows with no special-casing. But the docs still tell Windows users that auto-rewrite doesn't work and that they fall back to "CLAUDE.md injection mode". This PR closes that gap and adds a first-class Windows installer.

Why the docs are stale

• src/hooks/constants.rs: CLAUDE_HOOK_COMMAND = "rtk hook claude" (native Rust, not a shell script).
• src/hooks/init.rs run_default_mode() calls patch_settings_json_command(CLAUDE_HOOK_COMMAND, ...) on all platforms — there is no cfg!(windows) branch forcing run_claude_md_mode.
• src/hooks/hook_cmd.rs run_claude() reads stdin JSON / writes stdout JSON and already strips Windows UTF-8 BOMs.

So the "requires a Unix shell → falls back to CLAUDE.md" wording predates the migration to the native subcommand.

Changes

• install.ps1 (new): PowerShell installer that mirrors install.sh — resolves the latest release via the /releases/latest redirect (API fallback), downloads rtk-x86_64-pc-windows-msvc.zip, installs rtk.exe to %USERPROFILE%\.local\bin, and verifies PATH. Supports $env:RTK_VERSION / $env:RTK_INSTALL_DIR.
• README.md / INSTALL.md: add a Windows quick-install (irm ... | iex) and rewrite the Windows section so native auto-rewrite is the documented default; WSL is presented as optional.
• docs/troubleshooting.md, docs/supported-agents.md: replace the outdated fallback guidance with native-hook instructions, and honestly note that the Gemini hook is still a #!/bin/bash wrapper and needs WSL on native Windows until it migrates to rtk hook gemini.

Verification

• install.ps1 passes [System.Management.Automation.Language.Parser]::ParseFile (no syntax errors).
• End-to-end on native Windows 11 (PowerShell, no WSL) with the published rtk-x86_64-pc-windows-msvc.zip (v0.42.4):
  • rtk init -g → rtk init --show reports [ok] Hook: rtk hook claude, existing settings.json keys preserved (deep-merge).
  • echo '{"tool_name":"Bash","tool_input":{"command":"git status"}}' | rtk hook claude → updatedInput.command = rtk git status.
  • cargo test → rtk cargo test; unsupported commands (e.g. htop) pass through unchanged.

Scope / notes

• Docs + new installer only; no changes to Rust source or behavior.
• No tests added: install.ps1 is a thin installer with no Rust logic, consistent with the existing untested install.sh. Happy to add a CI lint (e.g. PSScriptAnalyzer) if maintainers want one.
• Out of scope (follow-up): migrating the Gemini hook from the bash wrapper to a native rtk hook gemini registration so it too works on native Windows.

[CLAassistant]

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