feat: add container deploy path (Containerfile, self-provisioning entrypoint, Forgejo registry push)

Containerfile

@@ -0,0 +1,22 @@
+# Default (non-rns) build only: microReticulum's cmake/C++ build isn't set
+# up for the musl toolchain alpine gives us, mirroring packages.static in
+# flake.nix. Use the Nix flake if you need the rns feature.
+FROM rust:1-alpine AS builder
+RUN apk add --no-cache musl-dev gcc
+WORKDIR /usr/src/bunshin
+COPY Cargo.toml Cargo.lock build.rs ./
+COPY src ./src
+RUN cargo build --release --locked
+
+FROM alpine:3.20
+RUN apk add --no-cache ca-certificates \
+    && adduser -D -h /data -u 10000 bunshin
+COPY --from=builder /usr/src/bunshin/target/release/bunshin /usr/local/bin/bunshin
+COPY docker-entrypoint.sh /usr/local/bin/docker-entrypoint.sh
+RUN chmod +x /usr/local/bin/docker-entrypoint.sh
+USER bunshin
+WORKDIR /data
+VOLUME /data
+EXPOSE 1961/tcp
+ENTRYPOINT ["docker-entrypoint.sh"]
+CMD ["serve", "--key", "/data/server.key", "--db", "/data/mail.db", "--host", "0.0.0.0", "--port", "1961"]