perf: remote browser CPU / zombie optimization

- Add tini (init: true in compose) to reap orphan Chromium processes
- Reduce screenshot push frequency (active 0.12→0.20s, idle 0.35→1.00s,
  deep idle 1.00→5.00s, backoff 0.60→2.00s)
- Add 5s timeout to screenshot in WebSocket push loop
- close() now wraps context.close() in asyncio.wait_for(10s)
  with browser.close() fallback on timeout
- Two-phase close logging (closing → closed / close_failed)
- Auth-capture sessions evicted after 10min TTL
- shutdown() with timeout protection and logging
- close_ok correctly tracks success through browser fallback path

Dockerfile

@@ -21,6 +21,9 @@ ENV PLAYWRIGHT_BROWSERS_PATH=/ms-playwright
 
 RUN sed -i 's|http://deb.debian.org|https://mirrors.aliyun.com|g; s|http://security.debian.org|https://mirrors.aliyun.com|g' /etc/apt/sources.list.d/debian.sources
 
+# Install tini as PID 1 to properly reap orphan Chromium zombie processes
+RUN apt-get update && apt-get install -y --no-install-recommends tini && rm -rf /var/lib/apt/lists/*
+
 # 系统依赖层：apt 包安装，缓存 deb 包避免重复下载
 RUN --mount=type=cache,target=/var/cache/apt \
     apt-get update \
@@ -59,4 +62,5 @@ ENV DATABASE_URL=sqlite:////app/data/app.db
 
 EXPOSE 8000
 
+ENTRYPOINT ["tini", "--"]
 CMD ["uvicorn", "app.main:app", "--host", "0.0.0.0", "--port", "8000"]