fix: set the role colour after .p10k.zsh, and add the config alias

The colour was in 05-prompt.zsh, before oh-my-zsh. That is right for ZSH_THEME
and wrong for everything else: ~/.p10k.zsh assigns
POWERLEVEL9K_CONTEXT_BACKGROUND itself and is sourced from 30-path.zsh, so the
role colour was overwritten before the first prompt was drawn. The isolated
test missed it because the throwaway HOME had no .p10k.zsh; on the real machine
the desktop came up with 0 instead of blue.

Theme before oh-my-zsh, colour after .p10k.zsh - two different constraints that
happen to pull in opposite directions.

The config alias was missing entirely. Without it the bare repository has no
front end, which makes the whole arrangement unusable. Guarded on ~/.cfg
existing so the alias does not appear on a machine that has not been set up.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

.config/zsh/rc.d/10-aliases.zsh

@@ -5,6 +5,18 @@
 # machine where lsd is not installed - the Mac, for one - and breaking ls is
 # the sort of thing that makes a shared dotfile repository feel like a mistake.
 
+# The dotfiles repository itself. A bare repo in ~/.cfg with $HOME as its work
+# tree, so "config" behaves like git for the configuration and the real git
+# stays out of the way in ordinary projects.
+#
+#   config status          what has drifted
+#   config add .zshrc      track a change
+#   config commit -m ...   and push as usual
+#
+# status.showUntrackedFiles=no is set in the repo, otherwise every file in
+# $HOME would show up as untracked.
+[[ -d "$HOME/.cfg" ]] && alias config='/usr/bin/git --git-dir=$HOME/.cfg/ --work-tree=$HOME'
+
 alias vi="nvim"
 alias ducks="du -cksh * | sort -rn | head"