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/CREDITS.md

@@ -0,0 +1,24 @@
+# Theme Asset Credits
+
+The NexusOS theme is assembled from original work plus assets adapted from the following upstream projects. All upstream sources are GPL-3.0 (or compatible), so the NexusOS theme inherits GPL-3.0.
+
+## Sources
+
+### WhiteSur GTK Theme — `gtk-2.0/`, `xfwm4/`
+- **Project**: https://github.com/vinceliuice/WhiteSur-gtk-theme
+- **Author**: Vince Liu (vinceliuice)
+- **License**: GPL-3.0
+- **Variant used as base**: `WhiteSur-Dark-purple`
+- **What we use**: The entire `gtk-2.0/` and `xfwm4/` directories are cloned verbatim from WhiteSur-Dark-purple. We rely on these for macOS-style window controls (stoplight buttons) and the GTK2 application skin.
+
+### Mint-Y Icon Theme — `NexusOS-icons/` (folder geometry reference)
+- **Project**: https://github.com/linuxmint/mint-y-icons
+- **Author**: Linux Mint team
+- **License**: GPL-3.0
+- **What we use**: Visual reference only for the folder shape language (flat folder with tab + lip). No PNGs are copied from Mint-Y; our folder set is regenerated from scratch via `NexusOS-icons-src/build.py` against a master SVG we authored.
+
+## NexusOS-original content
+- `gtk-3.0/*.css` — original work
+- `NexusOS-icons-src/*` and the rendered output in `NexusOS-icons/places/` — original work
+- The `n-small.png` badge composited into `folder-nexus-core` is the NexusOS logo at `nexus-core/assets/n-small.png`
+- `index.theme` files in each theme directory — original work