[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)

common/.config/fish/functions/fish_user_key_bindings.fish

@@ -0,0 +1,15 @@
+function fish_user_key_bindings
+    # free Ctrl+S from terminal flow control (XOFF) so it can be bound below
+    stty -ixon
+    fish_default_key_bindings -M insert
+    fish_vi_key_bindings --no-erase insert
+    bind -M default ctrl-a beginning-of-line
+    bind -M default ctrl-e end-of-line
+    bind -M insert ctrl-space accept-autosuggestion
+    bind -M insert ctrl-g 'git diff' repaint
+    bind -M insert ctrl-o execute yazi
+    bind -M insert ctrl-l clear-screen ls repaint
+    bind -M default ctrl-s copy-commandline
+    bind -M insert ctrl-s copy-commandline
+    bind -M search ctrl-s copy-commandline
+end