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/backup-smart.sh

@@ -0,0 +1,16 @@
+#!/bin/bash
+
+NEXUS_ROOT="$HOME/nexus-core"
+
+rsync -avz --delete \
+    --exclude='Promethean/' \
+    --exclude='models/blobs/' \
+    --exclude='ollama/' \
+    --exclude='management/Mint-Y-Nexus/' \
+    --exclude='interface/web/node_modules/' \
+    --exclude='interface/web/dist/' \
+    --exclude='runtime/' \
+    --exclude='__pycache__/' \
+    --exclude='*.pyc' \
+    -e ssh \
+    "$NEXUS_ROOT/" "router:/tmp/mnt/Wingdrive2/nexus-backup/"