🐛 Fix entrypoint hang and lost-interpreter bugs 🐛

- rootfs/usr/local/bin/entrypoint.sh:
  1. The "start all services" gate
     (`if [ "$START_SERVICES" = "yes" ] || [ -z "$1" ]`) always evaluated
     true on a first-run container regardless of $1, because
     START_SERVICES is force-set to "yes" whenever no PID file exists yet.
     Any command passed to `docker run` — `exec ...`, `sh -c ...`,
     `shell`, or an arbitrary program — was swallowed into the
     service-start+monitor branch before reaching the `case "$1"`
     statement that already handles those subcommands, hanging the
     container as a daemon instead of running the given command. Changed
     the condition to `if [ -z "$1" ]` so the daemon branch only fires
     when no command was given at all.
  2. The `*/bin/sh | */bin/bash | bash | sh | shell)` case branch
     unconditionally shifted $1 before `__exec_command "$@"` (a bare
     `exec "$@"`). For `docker run image sh -c 'cmd'` this turned the
     exec into `exec -c cmd` (command not found, exit 127) instead of
     `exec sh -c 'cmd'`. Split the branch: real interpreter names
     (*/bin/sh, */bin/bash, bash, sh) now pass through unshifted; the
     "shell" keyword (not a real interpreter) gets its own branch that
     shifts and prepends "sh" to any remaining args, or falls back to a
     bare `__exec_command` (exec bash -l) when none remain.
  Verified `bash -n` passes. Found and fixed upstream in
  dockersrc/go, confirmed identical in this repo's generated
  entrypoint.sh, and mechanically applied here with the same patch.

rootfs/usr/local/bin/entrypoint.sh

@@ -476,7 +476,11 @@ SKIP_SERVICE_START="no"
 [ "$2" = "init" ] && SKIP_SERVICE_START="yes" && CONTAINER_INIT="yes"
 # - - - - - - - - - - - - - - - - - - - - - - - - -
 # Start all services if no pidfile and not skipping
-if [ "$START_SERVICES" = "yes" ] || [ -z "$1" ]; then
+# Start all services only when no command was given at all — an explicit
+# command (exec, shell, tail, or an arbitrary program) must reach the case
+# statement below instead of being swallowed into daemon/monitor mode, even
+# on a first run where START_SERVICES is force-set to "yes"
+if [ -z "$1" ]; then
   if [ "$SKIP_SERVICE_START" = "no" ]; then
     [ "$1" = "start" ] && shift 1
     [ "$1" = "all" ] && shift 1
@@ -625,11 +629,25 @@ ssl)
   ;;
 # manage ssl certificate
 # Launch shell
-*/bin/sh | */bin/bash | bash | sh | shell)
-  shift 1
+# Launch shell — do not shift here: "sh -c 'cmd'" / "bash -c 'cmd'" needs the
+# interpreter name kept as argv[0] for __exec_command's `exec "$@"` to work;
+# shifting it away turned "sh -c 'cmd'" into `exec -c cmd` (command not found)
+*/bin/sh | */bin/bash | bash | sh)
   __exec_command "${@:-/bin/bash -l}"
   exit $?
   ;;
+# "shell" is a keyword, not a real interpreter — it must be shifted away, and
+# any remaining args need "sh" prepended so __exec_command's `exec "$@"` gets
+# a real interpreter instead of trying to exec "-c" as a program
+shell)
+  shift 1
+  if [ $# -eq 0 ]; then
+    __exec_command
+  else
+    __exec_command sh "$@"
+  fi
+  exit $?
+  ;;
 # execute commands
 exec)
   shift 1