[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)

lw/.config/kitty/host.conf

@@ -0,0 +1,2 @@
+# lw (laptop, smaller screen)
+font_size 9.0

lw/.config/kitty/music.conf

@@ -0,0 +1,13 @@
+# run with `kitty --session ~/.config/kitty/music.conf`
+# lw override: smaller split resizes than the shared version, to fit the laptop screen.
+
+new_tab music
+layout splits
+cd ~
+
+launch --var window=first cava
+launch --location=hsplit pyradio
+resize_window taller 10
+focus
+launch --location=vsplit pipes-rs
+resize_window wider 20