Adds new theme [bessertristan09/graphite-nightshade-theme] (#3428)

* Update theme

### 🌓 Adds "Graphite Nightshade" theme

**Repository:** https://github.com/bessertristan09/graphite-nightshade-theme  
**Maintainer:** Tristan Besser (@bessertristan09)

A refined and atmospheric dark theme for Home Assistant, based on the original Graphite Theme by Tilman Griesel — and reimagined with Figtree font, soft gradients, and full `ha-*` token support.

- ✅ HACS action passed
- ✅ Public GitHub repo with release
- ✅ Images in README
- ✅ Topics set

* Update theme

---------

Co-authored-by: Joakim Sørensen <joasoe@proton.me>

theme

@@ -14,6 +14,7 @@
   "basnijholt/lovelace-ios-light-mode-theme",
   "basnijholt/lovelace-ios-themes",
   "bbbenji/synthwave-hass",
+  "bessertristan09/graphite-nightshade-theme",
   "brezlord/BrezNET-iOS",
   "catppuccin/home-assistant",
   "chaptergy/homeassistant-theme-dark-pastel",
@@ -83,4 +84,4 @@
   "veniplex/hass-idx-theme",
   "williamahartman/noctis-solarized",
   "wowgamr/animated-weather-card"
-]
+]