[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/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