[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/fish/functions/__ssh_agent_is_started.fish

@@ -0,0 +1,23 @@
+function __ssh_agent_is_started -d "check if ssh agent is already started"
+	if test -n "$SSH_CONNECTION"
+		# This is an SSH session
+		ssh-add -l > /dev/null 2>&1
+		if test $status -eq 0 -o $status -eq 1
+			# An SSH agent was forwarded
+			return 0
+		end
+	end
+
+	if begin; test -f "$SSH_ENV"; and test -z "$SSH_AGENT_PID"; end
+		source $SSH_ENV > /dev/null
+	end
+
+	if test -z "$SSH_AGENT_PID"
+		return 1
+	end
+
+	ssh-add -l > /dev/null 2>&1
+	if test $status -eq 2
+		return 1
+	end
+end