Add Dockerfile and README

Prebuilt glibc image for pass-cli, so Alpine/musl-based CI jobs (e.g.
harmless-easy-bobcat's docker:cli-based deploy workflows) can pull and run
it without hitting missing glibc symbols.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

Dockerfile

@@ -0,0 +1,29 @@
+# pass-cli, glibc-linked, for hosts/CI where only an Alpine (musl) base is
+# otherwise available. pass-cli's Linux binary needs real glibc symbols
+# (fcntl64, __res_init, ...) that Alpine's gcompat/libc6-compat don't shim,
+# so it can't run in e.g. the docker:cli image directly.
+#
+# ENTRYPOINT is pass-cli itself, so `docker run this-image <args>` behaves
+# like `pass-cli <args>`. Callers who need to run their own script against
+# pass-cli instead (login, fetch a note, parse it, etc.) override the
+# entrypoint: `docker run --entrypoint sh this-image /path/to/script.sh`.
+
+FROM debian:bookworm-slim
+
+ARG PASS_CLI_VERSION=2.3.3
+ARG PASS_CLI_SHA256=b5b49a8b3fd0af8830c0c1979f28ea0c90ccece73f59023a8bca8245d4b68da9
+
+RUN apt-get update \
+    && apt-get install -y --no-install-recommends ca-certificates curl \
+    && curl -fsSL -o /usr/local/bin/pass-cli \
+         "https://proton.me/download/pass-cli/${PASS_CLI_VERSION}/pass-cli-linux-x86_64" \
+    && echo "${PASS_CLI_SHA256}  /usr/local/bin/pass-cli" | sha256sum -c - \
+    && chmod +x /usr/local/bin/pass-cli \
+    && apt-get purge -y curl \
+    && apt-get autoremove -y \
+    && rm -rf /var/lib/apt/lists/*
+
+# No kernel keyring in a container -- store the session on disk instead.
+ENV PROTON_PASS_KEY_PROVIDER=fs
+
+ENTRYPOINT ["pass-cli"]