place the selection panel beside what it describes

The panel was anchored to the right edge of the view, which is nowhere near
whatever the player just clicked. It now stands beside the selection: right of
it where it fits, otherwise left, otherwise the roomier side pushed inside the
view -- the one case where it covers part of what it describes.

Nothing told the panel where the selection was. The selection events carry ids
only, and the mode that separates a fresh selection from an expanded one is
consumed inside SelectionController before they are built, so the view now
publishes the selection's screen bounds itself, immediately before selecting and
only when the selection is starting. Freezing that rectangle is what holds the
panel still: it does not chase a scrolling view, a ship flying off, or a
selection being added to. Only the panel's own size still moves it, and even
then it keeps its side and the edge facing the selection.

The rectangles come from what the renderer was already computing for the
selection outlines, now shared rather than duplicated.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01JcReq7hVk4KUPhTDKWAG7K

src/ui/GameWorldView.h

@@ -226,6 +226,15 @@ private:
     // which is the only case that goes on to start a box drag.
     bool                     selectAtPoint(QPoint tile, QVector2D worldPos, bool additive);
     void                     selectInBox(bool additive);
+    // Publishes where on the screen the selection about to be made sits, so the
+    // selection panel can be placed beside it (REQ-UI-SELECTION-PANEL). Called with
+    // what is about to be selected, immediately before selecting it, and publishes
+    // nothing unless that selection is starting rather than growing.
+    void                     publishSelectionAnchor(
+                                 SelectionMode mode,
+                                 const std::vector<BuildingId>& buildings,
+                                 const std::vector<entt::entity>& actors,
+                                 const std::vector<entt::entity>& debris);
     void                     stepSpeed(int delta);
     void                     placeAtTile(QPoint tile);