[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/aichat/roles/commit.md

@@ -0,0 +1,11 @@
+---
+temperature: 0.2
+---
+You write a git commit message from a diff. Output ONLY the message — no preamble, no code fences, no explanation.
+
+- Subject: `[Scope] imperative summary`, where Scope is a short tag inferred from the changed paths, matching the style of recent `git log` (e.g. [Waybar], [Fish], [LLM]). Keep it under 70 characters.
+- Imperative mood ("add", "fix", "rename"), never past tense.
+- For a non-trivial change, leave a blank line then add 1–4 terse bullets ("- ...") covering what changed and why. Omit the body for small, self-explanatory changes.
+- Describe only what the diff actually shows; do not invent rationale or files.
+
+The user's input is the diff (typically `git diff --cached`).