feat(D.5.3a): selected-object meter — Health bar + name on the action bar

Port of gmToolbarUI::HandleSelectionChanged (acclient_2013_pseudo_c.txt:198635).
When the player selects a world object the action bar's bottom strip shows the
object name + (for player/pet/attackable targets) a live Health meter; deselect
clears it. Mana (#140) + stack slider deferred.

- SelectedObjectController (new): clear-then-populate on selection change; sets
  name (UiText child, VitalsController pattern), overlay state (ObjectSelected /
  StackedItemSelected via UiDatElement.ActiveState), shows the health meter and
  sends QueryHealth for health targets. Subscribes via a delegate seam (no
  GameWindow coupling).
- GameWindow: _selectedGuid field -> SelectedGuid property + SelectionChanged
  event (fires on actual change only); 3 write sites converted, reads untouched.
  All selection-write paths (LMB pick, Tab/Q, despawn-clear via Tick()) run on
  the render thread, so the event-driven UI mutation is single-threaded.
- WorldSession.SendQueryHealth (0x01BF) — wraps SocialActions.BuildQueryHealth.
- DatWidgetFactory.BuildMeter: handle the single-image toolbar meter shape
  (back-track on the element's own DirectState, fill on one Type-3 child). The
  sprites go in the TILE slot (DrawMode=Normal tiles to full bar geometry per
  UIElement_Meter::DrawChildren) — a left-cap assignment would gap/clamp a
  sub-140px sprite. Vitals 3-slice path unchanged.
- ToolbarController.HiddenIds: A1 (health) now owned by SelectedObjectController;
  A2 (mana) + A4 (stack) stay hidden (deferred) so their dat back-tracks don't
  render as stray empty bars.

Adversarial Opus review found + fixed: the mana-meter orphan (A2 left unhidden)
and the meter tile-vs-cap render bug (C1). Divergence rows AP-46 (health gate
approximation: IsLiveCreatureTarget vs IsPlayer||pet||attackable) + AP-47
(meter shown on select vs on UpdateHealth reply). Spec §5 corrected.

Build + full test suite green (2,684 passed / 4 skipped). Health meter render
fidelity (full-width fill + fraction mapping) pending the user's visual gate.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

src/AcDream.App/UI/Layout/ToolbarController.cs

@@ -35,10 +35,15 @@ public sealed class ToolbarController
         0x100006BC, 0x100006BD, 0x100006BE, 0x100006BF,
     };
 
-    // Elements hidden by default in retail gmToolbarUI::PostInit: the selected-object
-    // vitals meters (health/stamina/mana bars that track your target) and the stack slider.
+    // Elements hidden by default in retail gmToolbarUI::PostInit.
     // Ids confirmed from the toolbar LayoutDesc dump.
-    private static readonly uint[] HiddenIds = { 0x100001A1, 0x100001A2, 0x100001A4 };
+    // 0x100001A1 (health meter) is now OWNED by SelectedObjectController (D.5.3a) —
+    // it hides A1 at bind and shows it on a health-target selection, so A1 is removed
+    // from here to avoid double-ownership. 0x100001A2 (mana meter) and 0x100001A4
+    // (stack slider) are DEFERRED features (mana #140, stack-split UI) with no controller
+    // yet, so they stay hidden here — otherwise their dat back-track sprites render as
+    // stray empty bars on the toolbar.
+    private static readonly uint[] HiddenIds = { 0x100001A2, 0x100001A4 };
 
     // Four mutually-exclusive combat-mode indicator elements — exactly one visible at a time.
     // Index 0 = NonCombat (peace), 1 = Melee, 2 = Missile, 3 = Magic.