fix(win): prevent user PATH clobbering and normalize gateway PATH env

[vcfgv]

Summary

Fixes Windows PATH corruption and gateway startup regressions reported in #269, #440, #447.

Root Causes

• resources/cli/win32/update-user-path.ps1 could rewrite user Path unsafely and had a faulty Add-Type snippet.
• Gateway env setup used process.env.PATH directly; on Windows real key is often Path, which could drop inherited path entries.

Changes

• Added Windows-safe PATH helpers:
  • case-insensitive path key handling (Path/PATH)
  • deduplicate path keys before writing child env
  • prepend bundled bin safely
• Updated gateway launch/doctor env construction to use the new helpers:
  • electron/gateway/config-sync.ts
  • electron/gateway/supervisor.ts
• Hardened Windows PATH updater script:
  • read/write HKCU\Environment\Path with registry-kind awareness
  • refuse suspicious collapsing rewrites (anti-clobber guard)
  • fix Add-Type declaration to avoid compile errors
  • treat environment broadcast failure as warning, not fatal
• Added unit tests for env-path behaviors:
  • tests/unit/env-path.test.ts

Verification

• User PATH keeps existing entries after install/update.
• Only ClawX CLI path is added (no duplicate path-key pollution).
• openclaw --version works in new terminals.
• Gateway starts successfully on Windows without PATH-related failures.

Related Issues

• Closes It will clear the environment variables, this is a serious problem, please fix it 会把环境变量给清空，这个是严重问题，请修复 #269
• Closes 安装清理环境变量 #440
• Closes 更新0.2.1版本用户环境变量被强制清除 #447