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/ReplayPlaybackTest.cpp

@@ -77,12 +77,12 @@ TEST_CASE("parseCommand round-trips every command verb", "[replay]")
     ClearBeltTilesCommand clear;
     clear.tiles = { QPoint(0, 0), QPoint(-1, 4) };
 
-    DemolishCommand demolish;
-    demolish.id = 5;
+    DeconstructCommand deconstruct;
+    deconstruct.id = 5;
 
     for (const Command* command : { static_cast<const Command*>(&filters),
                                     static_cast<const Command*>(&clear),
-                                    static_cast<const Command*>(&demolish) })
+                                    static_cast<const Command*>(&deconstruct) })
     {
         const std::string text = serializeCommand(*command);
         const std::shared_ptr<Command> parsed = parseCommand(text);