feat(ui): Atlas Editorial redesign, dark mode, and new travel-plannin…

[Manuel10i]

…g features

Complete frontend redesign in the "Atlas Editorial" direction: warm paper/ink semantic tokens (terracotta + deep-teal accents), Fraunces display serif with Instrument Sans body and IBM Plex Mono details, cartographic grid/grain textures, and shared UI primitives (Button, Card, Sheet, CrowdCurve, ...).

Design system & theming

• Semantic light/dark tokens in globals.css via @custom-variant dark; "night atlas" dark mode follows the system, overridable via a toggle persisted to localStorage (pp_theme), with a no-FOUC inline script
• Map basemap swaps Positron/Dark Matter with the theme; label localization re-applied on style data; unified crowd palette (src/lib/crowd-palette.ts) replaces the previously triplicated green-red ramp

Pages

• Marketing (landing, 7 feature pages, destination, contact, privacy) rebuilt in the editorial language; mobile-first map screen with bottom control dock, thumb-size slider controls, and accessible bottom sheets
• Localized metadata (new "meta" namespace); German exonyms (Wien, Rom, ...) shown in search results, destination pages, compare, and the map sheet

New features

• Best-time finder (/best-time): 52-week crowd curve per destination with quietest/busiest weeks and map deep link
• Saved places + compare (/compare): local favourites, multi-series curve, shareable ?ids= links
• Quieter alternatives on destination pages (same category, calmer in peak)
• Map destination tap-sheet with year curve, save and share
• PWA: manifest, icons, apple-icon; native share with clipboard fallback; OG images for the site root and per destination (/api/og/destination)

Data fixes

• Venice was drastically under-modelled (2 travel patterns, metropolis default capacity): added 15 realistic source flows and capacityOverride 3.0 so it now reads packed May-Sep with a real winter dip
• API caches shortened to max-age=3600 + stale-while-revalidate so recomputed heatmap data reaches clients quickly

i18n: all new strings in en/de/es/fr, guarded by a messages-parity test. Tests: 272 passing (60+ new: crowd palette, theme provider, saved places, quiet alternatives, /api/busyness route, UI primitives).