dotcli: add dot setup folders (XDG short-name migration)

Adds a dot setup subcommand family (idempotent, re-runnable machine-setup
tasks) with a folders task that brings the 8 standard XDG user
directories under a fixed short-name convention (Desktop -> .desktop,
Documents -> doc, Downloads -> dwn, Music -> mus, Pictures -> pic,
Videos -> vid, Templates/Public -> .ignoreme), hardcoded rather than read
from ~/.config/user-dirs.dirs -- that file is a separate, manually
tracked dotfile whose values can drift or go stale, and the migration
must not depend on it being correct. The nested Pictures/Screenshots
folder is renamed to pic/screenshots in the same pass.

Content left behind in a legacy full-named folder by a fresh XDG-defaults
install -- empty or not -- is merged into its short-named replacement.
A same-named collision between a legacy folder and its target is never
overwritten: it is skipped, reported, and the legacy folder is left in
place rather than deleted while something in it could not be merged.
--dry-run previews what would move/skip without touching the filesystem.
xdg-user-dirs-update runs once afterward to notify running apps/portals.

.config/user-dirs.dirs

@@ -0,0 +1,16 @@
+# This file is written by xdg-user-dirs-update
+# If you want to change or add directories, just edit the line you're
+# interested in. All local changes will be retained on the next run.
+# Format is XDG_xxx_DIR="$HOME/yyy", where yyy is a shell-escaped
+# homedir-relative path, or XDG_xxx_DIR="/yyy", where /yyy is an
+# absolute path. No other format is supported.
+# 
+XDG_DESKTOP_DIR="$HOME/.desktop"
+XDG_DOWNLOAD_DIR="$HOME/dwn"
+XDG_TEMPLATES_DIR="$HOME/.ignoreme"
+XDG_PUBLICSHARE_DIR="$HOME/.ignoreme"
+XDG_DOCUMENTS_DIR="$HOME/doc"
+XDG_MUSIC_DIR="$HOME/mus"
+XDG_PICTURES_DIR="$HOME/pic"
+XDG_VIDEOS_DIR="$HOME/vid"
+XDG_PROJECTS_DIR="$HOME/wrk"