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/promethean-kitty.conf

@@ -0,0 +1,20 @@
+# Promethean Terminal — Project Nexus
+# Loaded via: kitty --config /home/jon/nexus-core/config/promethean-kitty.conf
+
+# Window title — disable kitty's shell integration title override
+# so the PS1 escape (\e]0;Promethean Terminal\a) controls the title
+shell_integration enabled no-title
+initial_window_title Promethean Terminal
+
+# Colors
+background #1a0030
+foreground #cccccc
+cursor #b040c0
+cursor_text_color #0d0010
+
+# Selection
+selection_background #3d0060
+selection_foreground #ffffff
+
+# Tab bar (hidden — single window use)
+tab_bar_style hidden