Initial commit: NexusOS project + desktop theme baseline

Captures the known-good state after theme consolidation and
consistency reconciliation:
- NexusOS GTK/xfwm4/icon theme assets (assets/themes, management/Mint-Y-Nexus)
- Tightened right-click menus, visible separators, no menu icons
- assets/themes/install-theme.sh: idempotent restore of all wiring
  (symlinks, xfconf xsettings+xfwm4, GTK 3/4 settings.ini)
- .gitignore excludes venv/ollama/models/runtime/db

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

assets/themes/_palette.py

@@ -0,0 +1,44 @@
+"""Shared color palette for NexusOS theme builds.
+
+Source of truth is NexusOS/gtk-3.0/colors.css. Keep these in sync.
+Hex strings have no leading '#'.
+"""
+
+# Brand
+BRAND_GREEN        = "8cc63f"
+BRAND_GREEN_LIGHT  = "b8e373"
+BRAND_GREEN_DARK   = "6ba62a"
+BRAND_PURPLE       = "88008f"
+BRAND_PURPLE_LIGHT = "a232a8"
+BRAND_PURPLE_DARK  = "5e0066"
+
+# Foundation
+BASE_BG        = "16181a"
+SURFACE_BG     = "1f2225"
+SURFACE_BG_ALT = "2a2e32"
+OVERLAY_BG     = "2e3236"
+BORDER         = "2e3236"
+BORDER_STRONG  = "3a3d41"
+
+# Text
+TEXT_PRIMARY      = "f2f2f2"
+TEXT_SECONDARY    = "a8a8a8"
+TEXT_DISABLED     = "6e7173"
+TEXT_ON_ACCENT    = "0a0a00"
+TEXT_ON_SELECTION = "ffffff"
+
+# Semantic
+SUCCESS = "27ae60"
+WARNING = "f67400"
+ERROR   = "da4453"
+
+
+def hex_to_rgb(h):
+    h = h.lstrip("#")
+    return (int(h[0:2], 16), int(h[2:4], 16), int(h[4:6], 16))
+
+
+def hex_to_hsv(h):
+    import colorsys
+    r, g, b = hex_to_rgb(h)
+    return colorsys.rgb_to_hsv(r / 255, g / 255, b / 255)