fix(docker): add tini init to reap zombie chromium processes

[manoj1919]

Summary

The container runs python as PID 1 (ENTRYPOINT ["python", "-m", "linkedin_mcp_server"]). When Patchright/Chromium helper processes exit, the kernel reparents them to PID 1, but Python never waitpid()s them, so they accumulate as zombie (<defunct>) chrome-headless processes for the life of the container.

This adds tini as a minimal init so PID 1 reaps orphaned subprocesses.

RUN apt-get update && apt-get install -y --no-install-recommends tini && rm -rf /var/lib/apt/lists/*
ENTRYPOINT ["tini", "--", "python", "-m", "linkedin_mcp_server"]

Fixing it in the image (rather than telling users to pass --init / compose init: true) means plain docker run consumers are covered too.

Verification

Built the image and confirmed PID 1 inside the container is now an init wrapping Python, with no zombies after exercising the Chromium-launching bridge flow:

PID 1: /sbin/...init -- python -m linkedin_mcp_server ...
process tree: init(1)---python(...)
zombies: none

Closes #477

Synthetic prompt

The Dockerized server leaks zombie chrome-headless processes because Python runs as PID 1 with no init to reap orphaned Chromium subprocesses. Add tini to the Dockerfile and make it the entrypoint (tini -- python -m linkedin_mcp_server) so PID 1 reaps zombies, fixing it at the image level so plain docker run users benefit without --init.

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