Challenge 1: Add a .dockerignore — Possible Solution
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node_modules
.git
.env
*.log

WHY THIS WORKS AS AN ANSWER
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node_modules is excluded because it's reinstalled fresh inside the
builder stage anyway (via npm install against package*.json) — sending
a potentially large, host-specific node_modules folder as part of the
build context wastes time and could even introduce platform-specific
binaries that don't match the container's own OS/architecture.

.git is excluded because the build never needs the full commit history
or Git metadata to actually build the application — including it only
bloats the build context unnecessarily.

.env is excluded specifically to prevent a local file possibly holding
real credentials from ever being accidentally COPYed into the image
during the build — the exact security concern this chapter (and
Chapter 6's broader credentials guidance) flagged directly, since
anything present in the build context is a candidate for accidentally
being copied into a layer.

*.log excludes local log files, which have no purpose inside a built
image and would just add unnecessary bulk to the build context sent to
the Docker daemon.