[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/shaders/pass_through.vert

@@ -0,0 +1,14 @@
+#version 330
+
+
+// Input vertex data, different for all executions of this shader.
+layout(location = 0) in vec3 vertexPosition_modelspace;
+
+// Output data ; will be interpolated for each fragment.
+out vec2 fragCoord;
+
+void main()
+{
+    gl_Position =  vec4(vertexPosition_modelspace,1);
+    fragCoord  = (vertexPosition_modelspace.xy+vec2(1,1))/2.0;
+}