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>

bin/promethean-terminal

@@ -0,0 +1,3 @@
+#!/bin/bash
+export GDK_PROGRAM_CLASS=promethean-terminal
+exec xfce4-terminal --working-directory ~ -e "bash --rcfile ~/.promethean_bashrc -i" "$@"