fix(ui): retail target-cursor shape (pending over UI, world-object driven) + visible UseDone refusals

Visual gate round 2 (user, retail oracle): the target cursor over UI must
be the 0x27 four-arrows PENDING cursor — retail's UpdateCursorState
(0x00564630) keys valid/invalid solely off the SmartBox found object,
i.e. the WORLD entity under the cursor. And "can't heal myself" turned
out to be TWO stacked causes, both fixed:

- Cursor: UI hover no longer forces TargetInvalid (that arm was a
  non-retail invention) and the doll/status-bar hover providers are
  gone (UiElement.UseTargetGuidProvider deleted). Valid/invalid now
  come from (a) a hovered occupied item slot's own item, or (b) the
  world entity under the cursor via a new worldTargetProvider — the
  B.4b screen-rect picker extracted into GameWindow.PickWorldGuidAtCursor
  and shared by click + hover.
- Self-heal: the world picker always skipped the local player
  (skipServerGuid), so clicking your own toon in target mode could
  never acquire self. Target-use picks now include self (retail lets
  you kit-heal yourself by clicking your character); plain selection
  keeps the exclusion. The doll click still self-targets.
- Silent refusals: the [use-target] log proved the UseWithTarget action
  WAS sent (kit 0x00220008 / TargetType 0x10, target self) — ACE
  refused with WeenieError.YouArentTrainedInHealing (0x04FC) and we
  never parsed UseDone (0x01C7). Now dispatched + surfaced as a chat
  line via WeenieErrorText (interim subset map, register AP-74, #166
  ports the retail String-table lookup).

Full suite green (3,295).

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

src/AcDream.Core.Net/Messages/WeenieErrorText.cs

@@ -0,0 +1,23 @@
+namespace AcDream.Core.Net.Messages;
+
+/// <summary>
+/// Interim WeenieError → display text. Retail resolves error codes through
+/// the portal String tables into lines like "You are not trained in
+/// healing!"; porting that lookup is #166 — until then this map (codes from
+/// ACE's <c>WeenieError</c> enum, texts phrased after the retail messages the
+/// enum names encode) covers the errors our current use/heal flows can
+/// produce. Register row AP-74. Unknown codes fall back to a generic line
+/// carrying the code so nothing is ever silently dropped again (the
+/// 2026-07-03 "kit did nothing" session was an unsurfaced 0x04FC).
+/// </summary>
+public static class WeenieErrorText
+{
+    public static string For(uint error) => error switch
+    {
+        0x001Du => "You're too busy!",                       // YoureTooBusy
+        0x04EBu => "You can't do that while in the air!",    // YouCantDoThatWhileInTheAir
+        0x04FCu => "You are not trained in healing!",        // YouArentTrainedInHealing
+        0x04FEu => "You can't heal that!",                   // YouCantHealThat
+        _ => $"You can't do that. (error 0x{error:X4})",
+    };
+}