Add config-defined tooltips to build and module buttons

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

bin/test/data/config/buildings.toml

@@ -84,6 +84,7 @@ cost = 25
 player_placeable = true
 construction_time_seconds = 15
 output_buffer_capacity = 20
+tooltip = "Drop-off point for salvage ships."
 surface_mask = [
   "SAA",
   "SAA>",

bin/test/data/config/modules.toml

@@ -1,5 +1,6 @@
 [[module]]
 id = "armor_plate"
+tooltip = "Adds a large flat bonus to hit points."
 unlock_at_station_level = -1
 surface_mask = ["OO"]
 materials = [{item = "iron_ingot", amount = 2}]