feat: custom recipe cover color/icon + mute auto placeholder palette (v0.51.0)

Two changes to the no-photo cover placeholder shipped last version:

1. Muted the gradient palette (100/40-opacity tints instead of solid -200/
   -950 stops) — the original was too saturated next to real cover photos
   in the same grid, per feedback.
2. New coverIcon/coverColor columns on recipes (nullable text, migration
   0048, additive-only) let the author pin a specific color+icon from the
   recipe editor instead of the automatic per-id pick. getRecipePlaceholder
   now checks these first, falling back to the deterministic hash pick when
   unset — existing recipes are unaffected until edited.

Wired coverIcon/coverColor through every explicit-column recipe select
that feeds a grid card (explore trending/recent, search, feed, for-you) —
the relational-query call sites (recipes page, collections, profile pages)
already return all columns and needed no changes.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

apps/web/app/api/v1/search/route.ts

@@ -137,6 +137,8 @@ export async function GET(req: NextRequest) {
       isBatchCook: recipes.isBatchCook,
       sourceUrl: recipes.sourceUrl,
       recipeType: recipes.recipeType,
+      coverIcon: recipes.coverIcon,
+      coverColor: recipes.coverColor,
       authorId: recipes.authorId,
       authorName: users.name,
       createdAt: recipes.createdAt,