[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/conf.d/fnm.fish

@@ -0,0 +1,7 @@
+# fnm — single init for all hosts (config.fish must NOT source fnm again:
+# every `fnm env | source` mints a fresh multishell dir onto PATH).
+# fnm may be pacman-installed (on PATH) or self-installed under ~/.local/share/fnm.
+test -d "$HOME/.local/share/fnm"; and fish_add_path -g "$HOME/.local/share/fnm"
+if command -q fnm
+    fnm env --use-on-cd --version-file-strategy local --shell fish | source
+end