[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/cava/themes/solarized_dark

@@ -0,0 +1,15 @@
+[color]
+background = '#001e26'
+foreground = '#708183'
+
+gradient = 1
+gradient_color_1 = '#268bd2'
+gradient_color_2 = '#6c71c4'
+gradient_color_3 = '#cb4b16'
+
+horizontal_gradient = 1
+horizontal_gradient_color_1 = '#586e75'
+horizontal_gradient_color_2 = '#b58900'
+horizontal_gradient_color_3 = '#839496'
+
+blend_direction = 'up'