Split schema.graphql and schema.resolvers.go into per-domain files

Move Query/Mutation field declarations from the monolithic schema.graphql
into each domain's .graphql file using extend type, so gqlgen places
resolvers in the matching *.resolvers.go files. Extract helper functions
into *_helpers.go files to prevent gqlgen from commenting them out.

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

backend/graph/steam.resolvers.go

@@ -1,28 +1,18 @@
 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"
-	"fmt"
 	"time"
 
 	"adam-french.co.uk/backend/graph/model"
 	"adam-french.co.uk/backend/services"
 )
 
-func mapSteamGames(games []services.SteamRecentGame) []*model.SteamGame {
-	result := make([]*model.SteamGame, len(games))
-	for i, g := range games {
-		result[i] = &model.SteamGame{
-			AppID:           g.AppID,
-			Name:            g.Name,
-			Playtime2Weeks:  g.Playtime2Weeks,
-			PlaytimeForever: g.PlaytimeForever,
-			HeaderImageURL:  fmt.Sprintf("https://cdn.akamai.steamstatic.com/steam/apps/%d/header.jpg", g.AppID),
-		}
-	}
-	return result
-}
-
 // SteamStatus is the resolver for the steamStatus field.
 func (r *queryResolver) SteamStatus(ctx context.Context) (*model.SteamStatus, error) {
 	if r.Store.SteamAPIKey == "" {