cosmos-hub (gaiad): add compose + init.sh + cometbft.Dockerfile

First pure-cosmos chain (validates the §2 cometbft-common.sh lib via real gaiad init).
Single-binary CometBFT client serving :26657 (dshackle chain=cosmos-hub). Statesync
bootstrap (polkachu) since genesis-replay across gaia governance upgrades is impractical.
gzipped genesis. v25.3.2 (live chain version; registry's v27.4.0 not on ghcr). Params
(chain_id/genesis_url/statesync_rpc/seeds/min_gas) from context.yml.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

cosmos/cometbft.Dockerfile

@@ -0,0 +1,11 @@
+ARG CL_IMAGE
+ARG CL_VERSION
+FROM ${CL_IMAGE}:${CL_VERSION}
+# Layer the shared CometBFT bootstrap lib + the chain init.sh onto the upstream
+# cosmos binary image (alpine-based, has sh+apk; runs nonroot by default — the compose
+# sets user: root so init.sh can apk-add curl and write the /root home).
+USER root
+COPY ./scripts/cometbft-common.sh /usr/local/bin/cometbft-common.sh
+COPY ./scripts/init.sh            /usr/local/bin/init.sh
+RUN chmod +x /usr/local/bin/init.sh /usr/local/bin/cometbft-common.sh
+ENTRYPOINT ["init.sh"]