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

Cargo.lock

@@ -2361,7 +2361,7 @@ dependencies = [
 
 [[package]]
 name = "zerogravity"
-version = "1.0.0"
+version = "1.0.1"
 dependencies = [
  "async-stream",
  "axum",