[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/.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}