[Sync] adopt unified stow layout from the private repo

Mirrors the private dots tree at 900bdda: one shared base plus per-host
overlays, replacing the old flat .config/ layout (last synced 2026-06-28).

- packages: common/ gui/ wm/ lw/ fl/ + install.sh and bin/ tooling (dotsync,
  reconcile-hyde.sh)
- new README (layout, deploy order, HyDE dependency), plus ToDo.md and
  HYDE-UPDATE.md
- current HyDE waybar rig (layouts/, cava), pi agent extensions, claude/
  config, tmux, presenterm, aichat roles
- drops stale duplicates and generated cruft that should never have been
  tracked: the second top-level .pi/ copy, btop.log, zellij config.kdl.bak,
  fish_variables, nvim codecompanion.lua
- .pi/agent/auth.json is gitignored now; auth.json.example ships instead
- fl/ and wm/ hypr themes/ stay untracked (HyDE-generated per machine, per
  the root .gitignore)

gui/.config/fish/conf.d/waybar.fish

@@ -0,0 +1,8 @@
+## gui package — waybar helpers. Lives in conf.d/ (fish sources every conf.d/*.fish),
+## NOT in host.fish: each host package ships its own host.fish, which stow deploys last
+## with --override — a gui/host.fish would be shadowed on every host that has one.
+
+# Reload the custom waybar (kill + relaunch, detached so it survives this shell).
+# Same invocation as userprefs.conf exec-once / the Ctrl+Alt+W bind. Killing waybar
+# also stops its cava child (cava-waybar.sh is a child of the bar).
+abbr wbar 'killall waybar; setsid -f waybar -c ~/.config/waybar/layouts/custom.jsonc -s ~/.config/waybar/layouts/custom.css'