[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/commit.md

@@ -0,0 +1,11 @@
+---
+description: Write a Conventional Commits message for the staged changes
+argument-hint: "[extra context]"
+---
+Inspect the staged changes with `git diff --cached` (and `git status` for context). Then write a single Conventional Commits message:
+
+- A `<type>(<scope>): <subject>` summary line, imperative mood, ≤72 chars (types: feat, fix, refactor, docs, chore, test, perf, build).
+- An optional short body explaining the *why* only when it isn't obvious from the diff.
+- Do NOT run `git commit`. Output only the message inside a code block so I can review it.
+
+Extra context to incorporate: ${1:-none}