Instead of generating/serving 20px placeholder images with blur CSS, extract
a perceptually accurate dominant color (Gaussian-weighted OKLAB average) and
use it as a solid background-color while the full image loads. Removes
placeholder image generation, blur CSS/JS, and placeholder directory references
across upload flows, API routes, service worker, and all card/hero components.
Adds admin bulk tool to backfill colors for existing recipes.
Consolidate duplicate recipe API routes into a single
api/[recipeLang=recipeLang]/ structure. Both /api/recipes/ and
/api/rezepte/ URLs continue to work via the param matcher. Shared
read endpoints now serve both languages with caching for both.
Also: remove dead code (5 unused components, cookie.js) and the
redundant cron-execute recurring payment route.
