Fluxer PostgreSQL→Cassandra migration tool

Type-aware migration from Fluxer's PostgreSQL fluxer_kv backend to the
native Apache Cassandra schema, plus scylla-feature image builds and a
full cutover runbook.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

images/Dockerfile.users.cassandra

@@ -0,0 +1,30 @@
+# SPDX-License-Identifier: AGPL-3.0-or-later
+# Identical to Dockerfile but compiled with --features scylla for Apache Cassandra support.
+# The feature is named "scylla" after the Rust crate — the runtime target is Cassandra.
+
+FROM rust:1-bookworm AS builder
+
+WORKDIR /usr/src/app
+
+COPY . .
+
+RUN cargo build --release -p fluxer-users --features scylla
+
+FROM debian:bookworm-slim
+
+ARG BUILD_VERSION=""
+
+WORKDIR /usr/local/bin
+
+RUN apt-get update && apt-get install -y --no-install-recommends ca-certificates && \
+	rm -rf /var/lib/apt/lists/*
+
+COPY --from=builder /usr/src/app/target/release/fluxer-users /usr/local/bin/fluxer-users
+
+ENV BUILD_VERSION="${BUILD_VERSION}"
+
+USER 65532:65532
+
+EXPOSE 8090
+
+CMD ["/usr/local/bin/fluxer-users"]