Restructure repo so the light variant installs as theme 'tintenblau'

omarchy-theme-install clones the repo into ~/.config/omarchy/themes/<name>
and omarchy-theme-set stages only the repo root. Moving the light variant
to the root makes 'omarchy theme install' produce a working theme; the dark
variant stays as tintenblau-dark/ subfolder.

zen.css

@@ -0,0 +1,18 @@
+:root {
+--color00: #f0ead9;
+--color01: #f0ead9;
+--color02: #f0ead9;
+--color03: #3a3f5a;
+--color04: #1e2a4a;
+--color05: #1e2a4a;
+--color06: #1e2a4a;
+--color07: #1e2a4a;
+--color08: #8a3028;
+--color09: #3a5a8a;
+--color0A: #3a5a8a;
+--color0B: #4a5a3a;
+--color0C: #3a5a6a;
+--color0D: #3a5a6a;
+--color0E: #5a4a72;
+--color0F: #8a3028;
+}