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.sh

@@ -0,0 +1,8 @@
+#!/bin/bash
+
+lftp sftp://router:2022 << 'LFTP'
+set sftp:connect-program "ssh -a -x -p 2022"
+set cmd:interactive yes
+mirror --reverse --delete --verbose --dereference --exclude "^Promethean/" --exclude "^models/blobs/" --exclude "^ollama/" --exclude "^interface/web/node_modules/" --exclude "^interface/web/dist/" --exclude "^runtime/logs/" --exclude "runtime/backend\.log$" --exclude "runtime/frontend\.log$" --exclude "__pycache__" --exclude "\.pyc$" /home/jon/nexus-core /Wingdrive2/nexus-backup
+quit
+LFTP