Replace mise-activate with simple wrapper scripts and ENV vars

The prompting for this change is to use mise within ksh/oksh without
having to rely on zsh (such as `zsh -c "mise activate zsh"` or
otherwise). I kind of like the simplicity of this, and then I can still
easily change versions as needed in a given project by sourcing a file
which exports different vars for target language versions, or I can just
do manual export commands from the shell.

src_files/shell/profile

@@ -41,6 +41,11 @@ export GIT_EDITOR="$EDITOR"
 # obsidian
 export OBSIDIAN_WORKSPACES_TO_CONFIGURE="$DIR_NOTES," # ,-delimitted list of dirs
 
+# language and tool vars
+export MISE_GO_VERSION="1.25.1"
+export MISE_PYTHON_VERSION="3.13.7"
+export MISE_RUBY_VERSION="3.4.7"
+
 # reaper
 export DIR_REAPER_PORTABLE_SHARED="$DIR_USER_OPT/reaper-portable/shared"
 export DIR_REAPER_PORTABLE_LINUX="$DIR_USER_OPT/reaper-portable/linux"