The previous build used IntersectionObserver to highlight whichever
section was in view. With nine sections of unequal heights and smooth-
scroll firing observer callbacks mid-scroll, the active highlight
drifted (clicking 'Konto' showed 'Soundboard' as active because the
last section never crossed the observer's 20%-30% band).
Switched to a tab pattern (macOS System Settings / Discord / GitHub
style): the sidebar selects ONE section, only that section renders.
`useState<TabId>` is the single source of truth; no observer, no
scrolling between sections, no anchor links to clash with HashRouter.
Mobile fallback (<lg) gets a `<select>` dropdown above the panel.
Drops the now-unused `id` prop from Section and removes the
IntersectionObserver effect.
byGalax
34b972ec2a