Add curl|sh installer targeting the KASI GitLab

install.sh fetches f5-connect + vpnc-dns-guard into ~/.local/bin from the
GitLab raw-file URLs (/-/raw/<ref>/<file>), seeds the config on first run,
and is idempotent (re-run to update). Supports F5_CONNECT_TOKEN for a
private repo and env overrides for base/ref/bindir. README documents the
one-liner plus a clone+symlink alternative.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>