[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/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`).