feat: remove cloakbrowser pip dependency, auto-download binary

feat: multi-target Dockerfile — gateway (498MB) and full (1.2GB)

perf: slim Dockerfile — multi-stage libgbm extraction saves ~200MB

feat: migrate to Patchright, add pool deploy templates

fix: pre-download Chromium as runtime user to avoid re-download on startup

initial release v0.1.0: headless browser rendering API