fix: cross-platform support + auto token from state.vscdb

- User-Agent now matches actual OS (macOS/Windows/Linux)
- grep -oP replaced with grep -oE for macOS BSD compat
- Port-killer gated with cfg(unix)/cfg(windows)
- zg binary: macOS uses launchctl, Windows uses schtasks
- Data dir mismatch fixed in mitm-redirect.sh
- Windows setup-windows.ps1 ProjectDir fixed
- README: token path, prerequisites updated
- setup-linux.sh: pre-flight dependency checks
- OAuth token auto-read from Antigravity state.vscdb
- Version bump to 1.0.1

scripts/setup-windows.ps1

@@ -4,7 +4,7 @@
 # Run as: powershell -ExecutionPolicy Bypass -File scripts\setup-windows.ps1
 
 $ErrorActionPreference = "Stop"
-$ProjectDir = Split-Path -Parent (Split-Path -Parent $PSScriptRoot)
+$ProjectDir = Split-Path -Parent $PSScriptRoot
 if (-not $ProjectDir) { $ProjectDir = (Get-Location).Path }
 
 # ── 1. Config directory ──