feat(apps): render /apps as an Android home-screen launcher on phones

[MichaelTaylor3d]

Apps → Android home-screen launcher (#51, extension popup #59)

The mobile Apps view now reads as a genuine Android launcher, and on phones it is the default landing — a phone visitor to explore.dig.net lands on the launcher (the "just like the home screen on your phone" promise), not the store.

What changed

• Clear 600px breakpoint. At or below 600px, /apps (and the phone landing /) render as a real home screen: a full-bleed, fixed violet→magenta ambient wallpaper, four even full-width columns of big rounded squircle icons floating with soft drop shadows, labels beneath, the grid flowing from the top, and a decorative bottom home-indicator pill. Above 600px the tidy centered desktop icon grid stands unchanged — the switch is crisp, not a gradual reflow.
• Width-aware landing. / on a phone (≤600px) defaults to the launcher; on desktop it defaults to the curated store. ?view=store|apps and a filter query (?q=/?category=) override the default, so both surfaces stay deep-linkable and the Store pill stays reachable from the launcher on a phone. /apps is always the launcher; /app/<slug> + not-found are unaffected. (Body is client-rendered → correct surface paints on first render, no flash.)
• AppIcon untouched. AppIcon is CRITICAL/reused across the store cards, featured carousel, and detail page — the launcher re-skins it via CSS only (never its API), per §2.0.
• New useLauncherViewport hook (mirrors useReducedMotion); ViewTabs gains a storeHref prop; wallpaper + home-indicator are decorative (aria-hidden).

Breakpoint

600px — ≤600 = phone launcher, >600 = desktop store/grid.

Blast radius (gitnexus, upstream)

• AppTile — LOW, 0 upstream callers (only AppsHomeScreen).
• AppsHomeScreen — LOW, 0 upstream (only the /apps+/ routes).
• AppIcon — CRITICAL, reused by AppCard/FeaturedSlide/AppDetailPage/AppTile across 7 flows → not modified; re-skinned via CSS descendant selectors only.
• App — routing gained the width-aware home surface; store view preserved. Change scoped to these.

Verification (this session)

• Unit + coverage: 199 tests pass, coverage 99.66% lines / 91.96% branches (gate ≥80%).
• a11y e2e: 70 Playwright tests pass — @axe-core/playwright WCAG 2.2 AA 0 violations on /apps in dark AND light, desktop AND mobile; launcher stays keyboard-operable + SR-sane; prefers-reduced-motion respected.
• typecheck clean, lint 0 errors, build OK.
• Visually inspected the launcher at 360 / 390 / 414 (dark + light) + desktop — unmistakably an Android launcher below the breakpoint, tidy store/grid above.
• i18n: no new user-facing copy (decorative chrome only) → all 14 locales stay complete (completeness test green).

Screenshots (mobile launcher)

390px dark	390px light

360px dark	414px dark	phone root / → launcher

Desktop stays the store/grid above the breakpoint: /apps desktop · / desktop → store

Version

minor 0.3.1 → 0.4.0 — notable additive visual/UX capability (new launcher presentation + width-aware landing), no breaking change.

Refs #51. Extension popup embed: #59.