[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/c2-worktree.fish

@@ -0,0 +1,30 @@
+function c2-worktree
+    if test (count $argv) -ne 1
+        echo "Usage: c2-worktree <branch-name>"
+        echo "Example: c2-worktree package/package-update"
+        return 1
+    end
+
+    set branch $argv[1]
+
+    set root (git rev-parse --show-toplevel)
+    or return 1
+    set dir $root/.worktrees/(basename $branch)
+
+    mkdir -p $root/.worktrees
+    or return 1
+
+    git checkout -b $branch
+    or return 1
+
+    git checkout master
+    or return 1
+
+    git worktree add $dir $branch
+    or return 1
+
+    cd $dir
+    or return 1
+
+    pnpm i
+end