Animations and transitions overhaul (Phases 0-5)

Refined-terminal motion language: per-route choreography, header continuity,
post-title morph, body reveal, theme crossfade, scroll stagger, heading
line-draw, palette open/close, copy-button spring, ToC indicator glide,
tag inverse-fill, focus rings, mobile tap pulse. -30% mobile durations,
no transform on mobile view transitions. 94 tests passing.

feat: JSON-LD (BlogPosting, Person, WebSite/SearchAction, BreadcrumbL…

…ist)

feat: custom brutalist 404