Merge upstream/development into feat-agent-zero-skills-upgrade

Accept upstream's architectural refactors: - Settings UI sections moved from Python to frontend components - User data consolidated under /usr directory - Inline settings modal replaced by stacked modal system - settings.js removed (moved to component stores) Conflicts resolved by accepting upstream for all 5 files. Our skills/backup features will be re-implemented using the new architecture. Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>