Add configurable stratum port (default 3333)

Exposes stratum-port in the StartOS config UI so users running
simpleproxy or another TCP forwarder can point Kamado at a
non-default port. Entrypoint substitutes the value into
ckpool.conf serverurl.

Also pins placeholder KAMADO_SHA in the Dockerfile — swap to a
real pushed commit before the first build.

docker_entrypoint.sh

@@ -40,6 +40,7 @@ BITCOIN_USER=$(q '.bitcoind.user')
 BITCOIN_PASS=$(q '.bitcoind.password')
 POOL_BTCADDRESS=$(q '.pool-address')
 POOL_IDENTIFIER=$(q '.pool-identifier')
+STRATUM_PORT=$(q '.stratum-port // 3333')
 DROPIDLE=$(q '.dropidle // 0')
 STARTDIFF=$(q '.startdiff // 16384')
 MINDIFF=$(q '.mindiff // 1000')
@@ -59,7 +60,7 @@ cat > "${CKPOOL_CONF}" <<EOF
  "btcaddress": "${POOL_BTCADDRESS}",
  "btcsig": "${POOL_IDENTIFIER}",
  "serverurl": [
-  "0.0.0.0:3333"
+  "0.0.0.0:${STRATUM_PORT}"
  ],
  "mindiff": ${MINDIFF},
  "startdiff": ${STARTDIFF},