Implement REQ-UI-BUILD-TOOLTIP and REQ-MOD-UI-MODULE-TOOLTIP: an optional tooltip string on BuildingDef and ModuleDef, parsed from buildings.toml and modules.toml and shown as the build/module button's hover tooltip. Omitted when unset. Author descriptions for all buildings and modules in the app config, and extend ConfigLoaderTest to cover the optional field. Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_01DZR44tA8sn4dPqDzAVXyps