[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/.pi/agent/prompts/review.md

@@ -0,0 +1,14 @@
+---
+description: Review the current diff for bugs and issues
+argument-hint: "[focus area]"
+---
+Review the current changes. Check both `git diff` (unstaged) and `git diff --cached` (staged). Focus on:
+
+- Correctness and logic bugs
+- Error handling and missing edge cases
+- Security issues (injection, secrets, unsafe input)
+- Anything that doesn't match the surrounding code's conventions
+
+List concrete findings as `file:line — issue — suggested fix`, ordered by severity. Be concise; skip praise. If nothing is wrong, say so.
+
+Extra focus this round: ${1:-general correctness}