Implement T hotkey for temporary blueprint from selection

Add a TemporaryBlueprintRequestedEvent emitted by GameWorldView on the T
key. BlueprintPanel handles it by building a blueprint from the current
selection (reusing createBlueprintFromSelection) and entering placement
mode via BlueprintPlacementRequestedEvent, without adding it to the list
or persisting it. Right-click exits and discards the temporary blueprint
through the existing exit path. No-op when nothing placeable is selected.

Implements REQ-UI-BLUEPRINT-TEMP.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01VGNNLeFWhVzvxkK9qVXP2K

src/ui/GameWorldView.cpp

@@ -56,6 +56,7 @@
 #include "EscapeMenuRequestedEvent.h"
 #include "TracePrintRequestedEvent.h"
 #include "BuildHotkeyPressedEvent.h"
+#include "TemporaryBlueprintRequestedEvent.h"
 #include "BossWaveUpdatedEvent.h"
 #include "BuilderModeExitedEvent.h"
 #include "BlueprintModeExitedEvent.h"
@@ -1582,6 +1583,13 @@ void GameWorldView::keyPressEvent(QKeyEvent* event)
         else if (m_blueprintMode.has_value()) { exitBlueprintMode(); }
         else                                  { toggleDemolishMode(); }
         break;
+    case Qt::Key_T:
+        // Request a temporary blueprint from the current selection (REQ-UI-BLUEPRINT-TEMP).
+        // The BlueprintPanel owns the selection and blueprint-capture logic; it decides
+        // whether anything placeable is selected and drives placement mode from there.
+        EventManager::getInstance()->sendEventImmediately(
+            std::make_shared<TemporaryBlueprintRequestedEvent>());
+        break;
     case Qt::Key_Escape:
         EventManager::getInstance()->sendEventImmediately(
             std::make_shared<EscapeMenuRequestedEvent>());