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/NexusOS-icons/index.theme

@@ -0,0 +1,75 @@
+[Icon Theme]
+Name=NexusOS
+Comment=NexusOS accent icon theme
+Inherits=Papirus-Dark
+Directories=16x16/apps,22x22/apps,24x24/apps,32x32/apps,48x48/apps,64x64/apps,128x128/apps,16x16/places,22x22/places,24x24/places,32x32/places,48x48/places,64x64/places,128x128/places
+
+[16x16/apps]
+Size=16
+Context=Applications
+Type=Fixed
+
+[22x22/apps]
+Size=22
+Context=Applications
+Type=Fixed
+
+[24x24/apps]
+Size=24
+Context=Applications
+Type=Fixed
+
+[32x32/apps]
+Size=32
+Context=Applications
+Type=Fixed
+
+[48x48/apps]
+Size=48
+Context=Applications
+Type=Fixed
+
+[64x64/apps]
+Size=64
+Context=Applications
+Type=Fixed
+
+[128x128/apps]
+Size=128
+Context=Applications
+Type=Fixed
+
+[16x16/places]
+Size=16
+Context=Places
+Type=Fixed
+
+[22x22/places]
+Size=22
+Context=Places
+Type=Fixed
+
+[24x24/places]
+Size=24
+Context=Places
+Type=Fixed
+
+[32x32/places]
+Size=32
+Context=Places
+Type=Fixed
+
+[48x48/places]
+Size=48
+Context=Places
+Type=Fixed
+
+[64x64/places]
+Size=64
+Context=Places
+Type=Fixed
+
+[128x128/places]
+Size=128
+Context=Places
+Type=Fixed