The continuous scroll was wrong for Instance — its sub-panels are
fundamentally different page types (user table, storage tool, bitrate
matrix, toggles). Revert to conditional rendering.
The hook now supports two modes:
- Scroll mode (default): smooth scroll + IntersectionObserver spy
- Tab mode (onNavigate callback): sidebar sub-links switch tabs
Instance uses tab mode. The scroll-spy infrastructure remains for
future panels that benefit from it (e.g. Account sections).
Also reverts GeneralPanel to sticky save bar since it's on its own
page again with no overlap risk.
Jannis Braun
437873c823