Rename Demolish to Deconstruct; add build button grid icons

Rename the Demolish* terminology to Deconstruct* across the simulation,
events, UI, tests, and docs (DemolishCommand and the DemolishMode* events
become their Deconstruct* equivalents), aligning with the deconstruction
queue at HEAD.

Add per-building SVG icons for the build button grid (REQ-UI-BUILD-GRID):
one color-chip icon per placeable building under data/icons/buildings,
loaded from disk at runtime and rendered with QtSvg onto each build button.
An unaffordable building's button shows a grey-recolored variant via a
QIcon Disabled-mode pixmap (REQ-UI-BUILD-DISABLED). Adds the Qt5::Svg
dependency and deploys Qt5Svg.dll.

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

src/test/SimulationTestAccess.h

@@ -33,7 +33,7 @@ struct SimulationTestAccess
         return sim.tryPlaceBuilding(type, anchor, rotation);
     }
 
-    static void demolish(Simulation& sim, BuildingId id) { sim.demolish(id); }
+    static void deconstruct(Simulation& sim, BuildingId id) { sim.deconstruct(id); }
 
     static void cancelDeconstruction(Simulation& sim, BuildingId id)
     {