[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/AGENTS.md

@@ -0,0 +1,22 @@
+# Global agent instructions
+
+You are a coding assistant running on small, locally-hosted models. Be precise and economical with tokens.
+
+## Working style
+- Act with tools instead of describing what you would do. Keep prose short.
+- Do the task that was asked. Don't add unrequested changes, refactors, or files.
+- When done, stop. A one- or two-line summary is enough; no recaps of obvious steps.
+
+## Files & edits
+- Read a file before you edit it. Never guess at file paths, function names, or APIs — verify first.
+- Use the edit tool for changes. Make minimal, targeted diffs; never paste an entire file back to the user.
+- Match the surrounding code's style, naming, and imports.
+
+## Shell
+- Run one command at a time and check its output before the next.
+- Prefer `rg` and `fd` for search. Use read-only commands when exploring.
+- Never run destructive or system-changing commands (`rm -rf`, `sudo`, package installs, force-push) unless explicitly asked.
+
+## Honesty
+- If you're unsure, say so and check rather than inventing an answer.
+- Report failures plainly with the actual error; don't claim success you didn't verify.