fix: varied gradient+icon placeholders for recipes without a cover photo (v0.50.2)

Replaces the single flat emoji-on-muted-bg fallback (same 🍽️/🍹 everywhere)
with a deterministic gradient + food/drink icon per recipe id — pulled from
a small curated palette/icon pool via a string hash, so it's stable across
re-renders but visually varied across a grid of photo-less recipes.

New shared lib/recipe-placeholder.ts + components/recipe/recipe-cover-
placeholder.tsx, applied everywhere the old inline emoji fallback lived:
recipe-grid-card.tsx, recipe-card.tsx, recipes-grid.tsx, and the public
profile page's recipe grid.

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

package.json

@@ -1,6 +1,6 @@
 {
   "name": "epicure",
-  "version": "0.50.1",
+  "version": "0.50.2",
   "private": true,
   "scripts": {
     "dev": "pnpm --filter web dev",