fix(docker): fail fast on build patch failures and add healthcheck

[devin-ai-integration]

Summary

The repo is just a Dockerfile, so the error-handling gaps are all in the build/run of the image. The dangerous ones are the sed patches: sed exits 0 when its pattern matches nothing, so if upstream nut v3.3 ever changes conf/nut.default.conf or requirements.txt, the build still succeeds and ships an image that scans the wrong directory or tries to install PyQt5 — a silent misconfiguration discovered only at runtime. Each patch now asserts its own result:

RUN sed -i '/scan/c "scan": ["\/titles"]' /root/nut/conf/nut.conf \
	&& grep -qF '"scan": ["/titles"]' /root/nut/conf/nut.conf
RUN sed -i -e '/pyqt5/d' -e '/qt-range-slider/d' /root/nut/requirements.txt \
	&& ! grep -qiE 'pyqt5|qt-range-slider' /root/nut/requirements.txt

Other propagation fixes:

• SHELL ["/bin/bash", "-euo", "pipefail", "-c"] so any future chained/piped RUN fails the build instead of returning the last command's status.
• apt-get autoremove → apt-get -y autoremove (previously it aborted with "Need to get..."/prompt semantics rather than doing its job) plus apt-get clean and removal of apt lists.
• test -f /root/nut/nut.py after extraction, so a changed archive layout fails at build time rather than as a container crash loop.
• PYTHONUNBUFFERED=1 / PYTHONFAULTHANDLER=1: tracebacks and fatal signals are otherwise buffered away and lost from docker logs when the server dies.
• HEALTHCHECK TCP-connects to 9000, so a dead or wedged server is reported instead of the container looking fine. --start-period=180s covers titledb loading (~90s observed).
• wget -O /tmp/nut.zip --tries=3, unzip -q, --no-install-recommends, --no-cache-dir.

Verification

• docker build succeeds; nut.conf contains "scan": ["/titles"].
• Container reaches health=healthy after startup, logs Server Starts - 0.0.0.0:9000.
• Negative test: a sed pattern that matches nothing now fails the build (exit code: 1) instead of passing silently.

Link to Devin session: https://app.devin.ai/sessions/166162ba454e4104bfe8ced74f39bb9a
Requested by: @eskwisit

[devin-ai-integration]

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