feat(server): add brand kit management and project binding

Add a brand kit domain with memory and postgres stores, a BrandKitService
for CRUD and resolution, and REST endpoints to list, upsert, and delete
brand kits. Projects can bind a brand kit whose resolved context and
reference images feed into the agent's long-term memory and design prompts.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

server/internal/logic/brand_kit_mapper.go

@@ -0,0 +1,25 @@
+package logic
+
+import (
+	"img_infinite_canvas/internal/domain/brandkit"
+	"img_infinite_canvas/internal/types"
+)
+
+func toAPIBrandKit(kit brandkit.Kit) types.BrandKit {
+	return types.BrandKit{
+		Id:        kit.ID,
+		Name:      kit.Name,
+		Document:  string(kit.Document),
+		IsDefault: kit.IsDefault,
+		CreatedAt: formatTime(kit.CreatedAt),
+		UpdatedAt: formatTime(kit.UpdatedAt),
+	}
+}
+
+func toAPIBrandKits(kits []brandkit.Kit) []types.BrandKit {
+	items := make([]types.BrandKit, 0, len(kits))
+	for _, kit := range kits {
+		items = append(items, toAPIBrandKit(kit))
+	}
+	return items
+}