[Sync] replace the flat layout with the unified stow tree

Supersedes the old flat .config/ layout (last published 2026-06-28) with the
private repo's structure: one shared base plus per-host overlays.

- packages: common/ gui/ lw/ fl/ wm/ plus install.sh and bin/ tooling
  (dotsync, reconcile-hyde.sh)
- new README covering the layout, deploy order and the HyDE dependency
- current HyDE waybar rig (layouts/, cava), pi agent extensions, claude/
  config, tmux, presenterm, aichat roles
- fish: kp (keepassxc-cli + fzf picker, db path from $KP_DB) and
  bind_M_n_history (alt+1..9 recalls the nth history entry)
- drops cruft that should never have been tracked: the duplicate top-level
  .pi/ copy, btop.log, zellij config.kdl.bak, fish_variables
- .pi/agent/auth.json is gitignored; auth.json.example ships instead

Host-specific work sessions and the personal backlog stay in the private
tree. Endpoint locators in the llamacpp/whisper guides are placeholders
($SERVER, <own-domain>) — the guides themselves stay, since they are the
useful part.

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