Implement building status light (REQ-UI-STATUS-LIGHT)

Add a per-building status light: a small circle drawn in the operational
building's upper-right corner (rotating with the building) so production
state is readable without selecting it.

- Sim: BuildingSystem::getProductionStatus classifies each building into
  Unconfigured/Producing/Starved/Blocked (nullopt for non-production
  types); Salvage Bay is a two-state special case (Producing with scrap,
  Starved when empty). Extracted shared predicates (gatherCandidateRecipes,
  recipeInputsAvailable, computeShipyardRequiredMaterials, hasInputsToStart)
  so tickProduction / tickShipyardProduction and the classifier stay in sync.
- UI: GameWorldView draws the circle, mapping status -> color from a new
  visuals.toml [status_light] section (grey/green/red/yellow + outline).
- Tests: getProductionStatus cases for every state, including red-over-yellow
  precedence and the auto-recipe/salvage-bay specials.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Y7N59FsLA5e2kuVdqe4Uhc

bin/app/data/config/visuals.toml

@@ -360,3 +360,17 @@ modal_dim      = "#00000099"   # semi-transparent black dim behind modal dialogs
 bg        = "#000000cc"
 fg        = "#ffffff"
 font_size = 14
+
+# -----------------------------------------------------------------------------
+# Building status light (REQ-UI-STATUS-LIGHT)
+#
+# Fill color per production state, drawn as a small circle in the building's
+# upper-right corner, plus the constant outline color.
+# -----------------------------------------------------------------------------
+
+[status_light]
+grey    = "#808080"   # no recipe/schematic selected
+green   = "#33cc33"   # producing (Salvage Bay: holding scrap)
+red     = "#cc3333"   # idle, input missing (Salvage Bay: empty)
+yellow  = "#e6c619"   # idle, output buffer full
+outline = "#000000"