[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/northern_lights.frag

@@ -0,0 +1,34 @@
+#version 330
+
+in vec2 fragCoord;
+out vec4 fragColor;
+
+// bar values. defaults to left channels first (low to high), then right (high to low).
+uniform float bars[512];
+
+uniform int bars_count;    // number of bars (left + right) (configurable)
+
+uniform vec3 u_resolution; // window resolution, not used here
+
+//colors, configurable in cava config file
+uniform vec3 bg_color; // background color(r,g,b) (0.0 - 1.0), not used here
+uniform vec3 fg_color; // foreground color, not used here
+
+void main()
+{
+    // find which bar to use based on where we are on the x axis
+    int bar = int(bars_count * fragCoord.x);
+
+    float bar_y = 1.0 - abs((fragCoord.y - 0.5)) * 2.0;
+    float y = (bars[bar]) * bar_y;
+
+    float bar_x = (fragCoord.x - float(bar) / float(bars_count)) * bars_count;
+    float bar_r = 1.0 - abs((bar_x - 0.5)) * 2;
+
+    bar_r = bar_r * bar_r * 2;
+
+    // set color
+    fragColor.r = fg_color.x * y * bar_r;
+    fragColor.g = fg_color.y * y * bar_r;
+    fragColor.b = fg_color.z * y * bar_r;
+}