refactor: organize components/app into topic folders

[starc007]

What

`components/app` had grown to 30+ flat files. Grouped into topic folders, pure move (no behavior change):

• `chrome/` — site shell/nav: site-header, site-footer, site-frame, site-sidebar, site-dock, site-search, mobile-nav, theme-provider, theme-toggle, header-tabs, page-transition, keyboard-shortcuts
• `docs/` — component doc-page pieces: code-block, copy-button, expandable-code, install-block, install-command, install-tabs, manual-install, component-card, new-badge
• `landing/` — homepage-only: hero, hero-preview-dock, landing-component-card, work-cta
• `analytics/` — google-analytics, json-ld
• `preferences/` — preferences-panel, preferences-provider
• `playground/` — untouched, already a folder

`icons.tsx` and `press-link.tsx` stay at root — both used across every group, no single topic owns them.

Also includes a small footer fix bundled in from the same working session: the footer's Components/Blocks columns now cap at 8 items (newest first) with a "View all (N)" link, instead of listing the entire growing registry.

Test plan

• `bun run check` clean (typecheck, lint, registry — 41 components)
• All 29 import sites across `app/`, `lib/`, `components/` updated to new paths