fix #382: chat-window indicator buttons invisible until first hovered

Root cause (found via reference-identity-verified live-DAT probing, not
a guess): the four main-chat-window indicator buttons (0x10000522-
0x10000525) resolve their own correct ActiveState="Normal" at
construction, then get blanked to "" moments later in the SAME
LayoutImporter.Build call. The indicator column's backing panel
(0x10000600) authors PassToChildren=true on its own empty DirectState
(confirmed live: States[0xFFFFFFFF].PassToChildren == true); when
LayoutImporter.BuildWidget's post-attach state reapply runs for that
panel, UiDatElement.TrySetRetailState cascades its DirectStateId to
every IUiDatStateful child, including the already-correctly-resolved
buttons. UiButton.TrySetRetailState's DirectStateId branch used to
accept that cascade because every button structurally carries a
DirectStateId entry in its States dict as a property bag (ToggleBehavior/
RolloverEnabled/etc), independent of whether it authors any blank
sprite, so TryFindState(DirectStateId) found that entry and blanked
ActiveState even with no "" media. A hover "fixed" it only because
UiButtonStateMachine.RequestedState resolves to the same canonical
Normal id regardless of PointerOver when RolloverEnabled is false.

Retail's own decompiled UIElement::SetState @0x00464e70 does the exact
same unconditional-commit-plus-cascade; retail avoids this specific bug
purely through construction timing (UIElement::Initialize's SetState
call precedes child-tree construction, so a cascade fired during import
always iterates zero children). Our port's LayoutImporter.BuildWidget
deliberately reapplies in the opposite order to give retained
PassToChildren tabs their authored child media, so this literal
state-machine port needed a compensating guard.

Fix: UiButton.TrySetRetailState's DirectStateId branch now requires
REAL "" media (HasStateMedia("")) before accepting the transition.
Scoped to UiButton only; UiDatElement's parallel branch and the cascade
mechanism are unchanged, so CharacterStatController's own
PassToChildren-driven chrome children are unaffected. Register row
AP-206 records the divergence from retail's literal unconditional-
commit semantics. Regressed by two fast unit tests in UiButtonTests.cs
(DirectStateCascade_WithoutRealMedia_DoesNotBlankAnAlreadyResolvedState,
DirectStateTransition_WithRealMedia_StillSucceeds) plus a live-mount
probe confirming all four buttons resolve ActiveState="Normal"
immediately after import against the real installed DAT.

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

docs/research/2026-08-11-campaign-op-test-script.md

@@ -476,6 +476,13 @@ regardless of the slider position.
 
 ### Filter checkboxes — live routing, per-window independence
 
+**Gate-4 re-test note (#382):** the main chat window's own four indicator
+buttons (the small LEDs that light up per floating-window 1-4 open/closed
+state) previously rendered NOTHING at rest — only a mouse hover revealed
+their orange numbered art. They now show their correct art immediately on
+window open, with no hover needed; report if any of the four is still
+blank before you've moved your mouse over it.
+
 8. **Open a floating chat window (Alt+1 through Alt+4, or the toolbar
    indicator buttons) and uncheck "Combat" in that SAME window's filter
    block on the Chat tab** (e.g. Floaty Chat Window 1's block if you opened