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>

management/Mint-Y-Nexus/index.theme

@@ -0,0 +1,94 @@
+[Icon Theme]
+Name=Mint-Y-Nexus
+Inherits=Mint-Y,Adwaita,gnome,hicolor
+Comment=Icon theme built for Linux Mint. Uses elements of Vibrancy and Moka.
+
+Directories=places/16,places/16@2x,places/22,places/22@2x,places/24,places/24@2x,places/32,places/32@2x,places/48,places/48@2x,places/64,places/64@2x,places/96,places/96@2x,places/128,places/128@2x
+
+[places/16]
+Size=16
+Context=Places
+Type=Fixed
+
+[places/16@2x]
+Size=16
+Scale=2
+Context=Places
+Type=Fixed
+
+[places/22]
+Size=22
+Context=Places
+Type=Fixed
+
+[places/22@2x]
+Size=22
+Scale=2
+Context=Places
+Type=Fixed
+
+[places/24]
+Size=24
+Context=Places
+Type=Fixed
+
+[places/24@2x]
+Size=24
+Scale=2
+Context=Places
+Type=Fixed
+
+[places/32]
+Size=32
+Context=Places
+Type=Fixed
+
+[places/32@2x]
+Size=32
+Scale=2
+Context=Places
+Type=Fixed
+
+[places/48]
+Size=48
+Context=Places
+Type=Fixed
+
+[places/48@2x]
+Size=48
+Scale=2
+Context=Places
+Type=Fixed
+
+[places/64]
+Size=64
+Context=Places
+Type=Fixed
+
+[places/64@2x]
+Size=64
+Scale=2
+Context=Places
+Type=Fixed
+
+[places/96]
+Size=96
+Context=Places
+Type=Fixed
+
+[places/96@2x]
+Size=96
+Scale=2
+Context=Places
+Type=Fixed
+
+[places/128]
+Size=128
+Context=Places
+Type=Fixed
+
+[places/128@2x]
+Size=128
+Scale=2
+Context=Places
+Type=Fixed