feat: add shell profiles for zsh, sh, csh/tcsh

- profile.bash: simplified preexec_init (early return), extracted
  ___keep_complete helper for @/@@ completion wrappers
- profile.zsh: add-zsh-hook preexec, wrapper function, @/@@ aliases,
  completions via compdef
- profile.sh: POSIX-compatible for sh/dash/ksh. Wrapper function,
  @/@@ aliases. No preexec or completions.
- profile.csh: alias-based keep wrapper, @/@@ aliases. No preexec
  or completions.
- modulefile: adds KEEP_SH_PROFILE, KEEP_ZSH_PROFILE, KEEP_CSH_PROFILE
- README: updated Shell Integration table and Shell Completion section

profile.csh

@@ -0,0 +1,11 @@
+#!/bin/csh
+# Profile for csh and tcsh.
+# Preexec hooks are not available; KEEP_META_command is not set.
+
+if ( ! $?KEEP_META_tty ) then
+  setenv KEEP_META_tty `tty`
+endif
+
+alias keep 'env KEEP_META_tty=${KEEP_META_tty} command keep \!*'
+alias @ 'keep --save \!*'
+alias @@ 'keep --get \!*'