fix(docker): add libz.so.1 to runtime image

The Chainguard glibc-dynamic runtime introduced in 8b520a8 ships only
glibc + libgcc + ca-certs + tzdata. nodedb's binary dynamically links
libz.so.1 (transitively via crates that default to system zlib, e.g.
flate2 with its default `zlib` feature), causing immediate startup
failure on the v0.1.0 image:

  error while loading shared libraries: libz.so.1:
  cannot open shared object file: No such file or directory

This patch copies libz from the Debian builder stage into /usr/lib of
the runtime, where the dynamic linker finds it via the default search
path. The source path glob covers both amd64 and arm64 multiarch
layouts — only the building arch's directory exists per matrix job.

Long-term cleanup options (any of which would let us drop this COPY):

  * Switch flate2 (and any other zlib-using deps) to `rust_backend`,
    making libz a build-time C lib statically linked into the binary.
  * Or vendor libz via the `libz-sys` `static` feature.
  * Or move runtime to `cgr.dev/chainguard/wolfi-base` + `apk add zlib`.

Reproducer (with v0.1.0 image):

  docker run --rm farhansyah/nodedb:0.1.0

Author: emanzx

Dockerfile

@@ -45,6 +45,23 @@ USER nonroot:nonroot
 
 COPY --from=builder --chown=nonroot:nonroot /build/target/release/nodedb /usr/local/bin/nodedb
 
+# nodedb dynamically links libz.so.1 (transitively via crates that default to
+# system zlib — e.g. flate2 with its default `zlib` feature). Chainguard's
+# glibc-dynamic ships only glibc + libgcc + ca-certs + tzdata, so the runtime
+# fails immediately with: "error while loading shared libraries: libz.so.1:
+# cannot open shared object file: No such file or directory".
+#
+# Copy the Debian builder's libz into a default ld.so search path. The glob
+# covers both amd64 and arm64 — per-arch builds only see their own multiarch
+# directory, so exactly one match per build.
+#
+# Long-term cleanup options (any of these would let us drop this COPY):
+#   * Switch flate2 (and any other zlib-using deps) to the `rust_backend`
+#     feature so libz becomes a build-time C lib statically linked.
+#   * Or vendor libz via the `libz-sys` `static` feature.
+#   * Or move runtime to `cgr.dev/chainguard/wolfi-base` + `apk add zlib`.
+COPY --from=builder /lib/*-linux-gnu/libz.so.1 /usr/lib/libz.so.1
+
 # Bind to all interfaces (required for Docker port mapping)
 # Point data dir at the declared volume
 ENV NODEDB_HOST=0.0.0.0 \