feat(server/stats): stats-overhaul Phase2 — 每设备归因 + GB 综合配额

服务端记账从「账户」细到「每设备」(每设备独立 dp_uuid),配额单位分钟→GB
按账户综合卡控。000015_per_device_usage 迁移(mysql+sqlite 双份):devices.dp_uuid
+ usage_device_daily 表 + plans.daily_mb。handler_grpc 按 dp_uuid 回映射
(user_id,device_id) 双写账户+每设备;usage 服务/handler 暴露 /v1/usage(/devices)。
含 sqlite_per_device / usage handler 测试。

注:此迁移 prod 已 migrate up 运行、部署二进制已内嵌;本次补提交使 git 与线上一致。

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

server/internal/store/sqlite_migrate_test.go

@@ -29,8 +29,8 @@ func TestSQLiteMigrateUpDown(t *testing.T) {
 	if dirty {
 		t.Fatalf("schema dirty after MigrateUp")
 	}
-	if v != 14 {
-		t.Errorf("version = %d, want 14", v)
+	if v != 15 {
+		t.Errorf("version = %d, want 15", v)
 	}
 
 	// 2. Core tables exist.
@@ -38,7 +38,7 @@ func TestSQLiteMigrateUpDown(t *testing.T) {
 		"users", "devices", "plans", "subscriptions", "code_batches", "codes",
 		"usage_daily", "audit_log", "providers", "nodes", "node_events",
 		"directory_version", "provision_idempotency", "replacements", "admins",
-		"connect_credentials",
+		"connect_credentials", "usage_device_daily",
 	} {
 		var name string
 		err := db.QueryRow(