[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/extract.fish

@@ -0,0 +1,23 @@
+function extract --description 'Extract any archive'
+    switch $argv[1]
+        case '*.tar' '*.tar.*' '*.tgz' '*.tbz2' '*.txz' # tar autodetects compression
+            tar xf $argv[1]
+        case '*.zip'
+            unzip $argv[1]
+        case '*.rar'
+            unrar x $argv[1]
+        case '*.7z'
+            7z x $argv[1]
+        case '*.gz'
+            gunzip -k $argv[1]
+        case '*.xz'
+            unxz -k $argv[1]
+        case '*.zst'
+            unzstd $argv[1]
+        case '*.bz2'
+            bunzip2 -k $argv[1]
+        case '*'
+            echo "Unknown extension: $argv[1]"
+            return 1
+    end
+end