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>

nexus-control-panel.desktop

@@ -0,0 +1,9 @@
+[Desktop Entry]
+Type=Application
+Name=Nexus Control Panel
+Comment=Launch the Nexus Control Panel for Project Nexus
+Exec=/home/jon/nexus-core/Promethean/bin/python /home/jon/nexus-core/management/controlpanel.py
+Icon=/home/jon/nexus-core/assets/n small.png
+Terminal=false
+Categories=Development;Utility;
+StartupWMClass=Tk