superwow: the chat bubbles are widgets — CREATE_CHATBUBBLE and pfUI's skin

The last real SuperWoW feature, and one piece of work closed three
things: `CREATE_CHATBUBBLE` (which could not honestly be fired, because
its payload can only be the bubble), `C_ChatBubbles.GetAllChatBubbles`
(which answered an empty list, truthfully, for the same reason) and
pfUI's whole bubble skin, which walks that list.

`benilla-ui`'s `script/chat_bubble.rs` is a pool of real frames —
anonymous WorldFrame children with a backdrop (`0x4b0a35` IS
`SetBackdrop`), a tail texture and a FontString, which is what the
reference's own `CGChatBubbleFrame` is and how addons of the era found
bubbles before SuperWoW published the event. The app keeps everything a
bubble's existence depends on — the spawn gate, the lifetime, the fade,
the range re-test, the stacking sort and the text measurement that sizes
the frame — and hands it over as `BubbleState`: the same split
`vplates.rs` already makes for the plates, so the engine decides what is
on screen, the widget layer decides what Lua sees, and neither can
disagree about a bubble because there is one feed.

Three things improved by the move rather than being preserved by it:

- The bubbles sit at frame levels 2, 3, 4… over the V-plates at level 1,
  which is the reference's own order (`0x4b12d5`-`0x4b1312`). The quad
  band had them UNDERNEATH — a deviation `overlay_z` carried in a
  comment. That band is gone and the lane is down to one tenant.
- The art is loaded, tiled and bleed-inset by the UI pass like any other
  frame's, so this file drops its own texture resource and its own
  half-texel inset helper.
- The system moved BEFORE the paint. It sat in `UiQuadAppend`, the window
  *after* the extract: right for an appender, a frame late for a feed.

The test that matters transcribes pfUI's own `ScanBubbles` loop — it
finds the FontString with the line and its chat-type colour, blanks the
one Texture region and parents its own frame to the bubble — and then
checks the EXTRACT for drawn quads: both backdrop halves, the tail, and
the text at the em the app measured the box with. A test that only
checked the widgets would have passed with nothing on screen.

Two architectural gates caught this and both were answered rather than
silenced. The one-shot gate: `drive_bubbles` now holds the VM and drains
a queue, so it is EXEMPT with the argument — the queue's product is
app-side state, the widget sync is idempotent and binds on the first
frame there is a WorldFrame, and gating the system instead would pile
lines up and spawn them all at once with fresh lifetimes. The VM wall:
its ceiling rises by one with the reason, which is that this file is
`vplates.rs`'s exact twin.

`CREATE_CHATBUBBLE` fires per APPEARANCE, not per pool slot ever built —
the opposite of `NAME_PLATE_CREATED`'s rule, because a recycled frame has
been re-anchored, re-sized and re-texted since it was last seen.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01SgstFWtn1RxEJ5kVrpgYwn

crates/benilla-app/src/ui_script/reference_ui.rs

@@ -2634,6 +2634,14 @@ mod tests {
                 "SuperWoW's own event, the one every cast-tracking addon on this realm registers; \
                  1.12 reports another unit's casts nowhere at all",
             ),
+            (
+                "CREATE_CHATBUBBLE",
+                "SuperWoW: a chat bubble appeared, `arg1` its frame — the third and last of its \
+                 events, and the one that could not honestly be fired until the bubbles were \
+                 widgets (`benilla-ui`'s `script/chat_bubble.rs`) rather than overlay quads. 1.12 \
+                 publishes no bubble edge at all: pfUI's own workaround is to re-scan the whole \
+                 bubble list the frame after every say, yell and monster line",
+            ),
             (
                 "RAW_COMBATLOG",
                 "SuperWoW: every combat-log line twice over — as the player reads it, and with \