Consolidate frontend REST calls with GraphQL

Replace 5 separate REST calls on home page load with a single GraphQL
query. Add homeData store that fetches posts, favorites, activities,
spotify, and auth in one request. Convert all admin mutations and
auth flows to use GraphQL. Add album images to Spotify GraphQL schema.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

backend/graph/post.resolvers.go

@@ -0,0 +1,22 @@
+package graph
+
+// This file will be automatically regenerated based on the schema, any resolver
+// implementations
+// will be copied through when generating and any unknown code will be moved to the end.
+// Code generated by github.com/99designs/gqlgen version v0.17.88
+
+import (
+	"context"
+
+	"adam-french.co.uk/backend/models"
+)
+
+// ID is the resolver for the id field.
+func (r *postResolver) ID(ctx context.Context, obj *models.Post) (int, error) {
+	return int(obj.ID), nil
+}
+
+// Post returns PostResolver implementation.
+func (r *Resolver) Post() PostResolver { return &postResolver{r} }
+
+type postResolver struct{ *Resolver }