feat(ui): port retail toolbar ammo count

Resolve stacked thrown weapons versus separately equipped missile ammo exactly like gmToolbarUI, normalize a zero stack to one, and refresh the authored missile indicator from equipment and stack events. Keep the decision in pure Core with retained and real-DAT conformance coverage.

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

docs/research/2026-07-11-retail-toolbar-ammo-pseudocode.md

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+# Retail toolbar ammunition pseudocode
+
+## Named-retail oracle
+
+- `gmToolbarUI::UpdateAmmoID @ 0x004BF210`
+- `gmToolbarUI::UpdateAmmoNumber @ 0x004BE9E0`
+- `gmToolbarUI::RecvNotice_ServerSaysMoveItem @ 0x004BF2B0`
+- `gmToolbarUI::RecvNotice_ItemAttributesChanged @ 0x004BF8F0`
+- `ACCWeenieObject::GetObjectAtLocation @ 0x0058CE00`
+
+The Binary Ninja text corrupts the second `GetObjectAtLocation` constant into a
+string literal. The surrounding branch, retail `INVENTORY_LOC` header, ACE
+`EquipMask`, and holtburger equipment model agree that the two locations are
+`MISSILE_WEAPON_LOC = 0x00400000` and `MISSILE_AMMO_LOC = 0x00800000`.
+
+## Literal pseudocode
+
+```text
+UpdateAmmoID:
+    oldAmmoID = ammoID
+    ammoID = 0
+    player = GetWeenieObject(playerID)
+    if player exists:
+        weaponID = player.GetObjectAtLocation(MISSILE_WEAPON_LOC, priority=0)
+        if weaponID != 0:
+            weapon = GetWeenieObject(weaponID)
+            if weapon exists and weapon.maxStackSize > 1:
+                ammoID = weaponID
+
+        if ammoID == 0:
+            ammoID = player.GetObjectAtLocation(MISSILE_AMMO_LOC, priority=0)
+
+        if ammoID != oldAmmoID:
+            UpdateAmmoNumber()
+
+UpdateAmmoNumber:
+    text = ""
+    ammo = GetWeenieObject(ammoID)
+    if ammo exists:
+        count = ammo.stackSize
+        if count == 0:
+            count = 1
+        text = decimal(count)
+    SetText(toolbarElement 0x10000194, text)
+```
+
+`GetObjectAtLocation` walks the player's ordered inventory-placement list and
+returns the first entry whose location mask intersects the requested mask.
+Stackable missile weapons therefore display their own count (thrown weapons);
+ordinary launchers display the separately equipped ammunition stack.
+
+Move notices touching player equipment locations `0x00C00000` recompute the
+ammo object ID. Attribute/stack changes for the current ammo object refresh its
+number. Player-description arrival also performs an initial resolution.
+
+## Port boundary
+
+`ToolbarAmmoPolicy` is pure Core logic over the ordered player placement list.
+`ToolbarController` owns repository event subscriptions and writes the resulting
+decimal label into authored element `0x10000194`. Missing ammo is an empty label.