feat: merge Explore and Activity Feed, unify recipe cards

Explore and Feed covered overlapping ground (recommendations, following,
trending) in two separate places with three different card designs.
Explore now hosts Discover/Following/For You tabs, and every recipe
card everywhere on the page matches the Recipes page's cover-photo
card instead of the old text-only search result.

v0.36.0

apps/web/messages/en.json

@@ -504,6 +504,7 @@
   },
   "explore": {
     "title": "Explore",
+    "tabDiscover": "Discover",
     "searchPlaceholder": "Search recipes and people…",
     "peopleHeading": "People",
     "recipesHeading": "Recipes",
@@ -934,6 +935,7 @@
     "title": "Feed",
     "followEmpty": "Follow chefs to see their recipes here.",
     "followEmptyDescription": "Your following feed fills up as soon as you follow a few people.",
+    "followEmptyDescriptionExplore": "Search for people above and follow a few chefs to see their recipes here.",
     "findPeople": "Find people to follow",
     "noNew": "No new recipes from people you follow.",
     "following": "Following",