fix(ui): finish retail stack selector polish

Keep the horizontal thumb at its raw pointer position so both endpoints are reachable, honor the stack entry's authored right alignment, and preserve PublicWeenieDesc plural names from CreateObject through the object table. Port retail's singular s/es fallback when no plural was sent.

Co-Authored-By: Codex <codex@openai.com>

docs/research/2026-07-10-retail-toolbar-interaction-pseudocode.md

@@ -507,7 +507,8 @@ HandleSelectionChanged():                                 // 0x004BF380
     if object missing: return
 
     set selected name:
-        normal object: name, or `"%d %hs"` (count then name) when stacked
+        normal object: NAME_APPROPRIATE, or `"%d %hs"` (count then appropriate
+        name) when stacked
         owned coinstack: formatted coin total/name path
 
     splitSize = 1
@@ -561,6 +562,16 @@ RecvNotice_UpdateItemMana(id, fraction, valid):             // 0x004BD0C0
 
 ### 5.4 Stack editing
 
+`ACCWeenieObject::GetObjectName(NAME_APPROPRIATE) @ 0x0058E6E0` selects
+`PublicWeenieDesc._plural_name` whenever `_stackSize > 1`. If the optional plural
+string is empty, retail copies the singular and appends `s`, or `es` when the
+singular already ends in lowercase `s`. The CreateObject WeenieHeader carries the
+explicit plural as flag `0x00000001`, before ItemsCapacity.
+
+The stack entry's authored DAT horizontal justification is Right. Its number is
+therefore right-aligned against the slider's left edge rather than drawn from the
+entry's left edge.
+
 - `RecvNotice_SplitStack(selectedId)` activates and selects all text only when the
   selected object still has a stack size greater than one.
 - On entry activation, select all text.
@@ -583,6 +594,11 @@ splitSize = clamp(1 + floor(positionMillis * maxSplitSize / 1000),
 The apparently odd extra one is verbatim retail behavior. Static cdb disassembly
 of the matching v11.4186 binary also pins the stack-name format string at
 `0x007B4738` to `"%d %hs"` and the numeric-entry format at `0x007A0184` to `"%d"`.
+While the pointer is moving, the scrollbar retains its own normalized position and
+the toolbar only rewrites the entry text. Selection refresh or entry deactivation
+explicitly writes attribute `0x86 = splitSize/maxSplitSize`. Consequently a pointer
+drag can remain at exact position `0` (quantity 1) or `1` (the maximum), rather than
+being redrawn from the quantized quantity during the drag.
 
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