Finish Phase 1.2 HUD: selection wiring, command grid context, build progress bar

- Builder.DisplayName: stub property ("Builder (P{n})") for portrait label; swaps
  to real player name when MatchState lands in Phase 1.3
- HUDController: subscribe SelectionState.OnSelectionChanged in OnEnable/OnDisable;
  HandleSelectionChanged drives portrait label + grays out command grid when nothing
  is selected; Start() seeds initial state in case builder auto-selected before Start
- BuildSiteVisual: ComputeProgressNormalized() public API ([0,1], safe on any client);
  OnNetworkSpawn spawns a non-networked BuildProgressBar child
- BuildProgressBar: new world-space uGUI Canvas bar; green while Constructing, yellow
  while Paused, hidden while Queued; billboards to Camera.main each LateUpdate;
  auto-destroyed when parent BuildSiteVisual despawns

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Assets/_Project/Scripts/Gameplay/Builder.cs

@@ -156,6 +156,17 @@ namespace TD.Gameplay
         /// <summary>Maximum jobs allowed in the queue.</summary>
         public int MaxQueueDepth => settings.maxQueueDepth;
 
+        /// <summary>Display name shown in the HUD portrait. Stub until MatchState provides player names.</summary>
+        public string DisplayName
+        {
+            get
+            {
+                PlayerSlot slot = OwnerToSlot(OwnerClientId);
+                int n = (int)slot;
+                return n >= 1 && n <= 9 ? $"Builder (P{n})" : "Builder";
+            }
+        }
+
         /// <summary>True if a tile is currently part of any queued or constructing job.</summary>
         /// <remarks>
         /// Used by <c>TowerPlacementManager</c> to reject placement on tiles already