Everwood: the HD/OctoWoW line of benilla, imported onto upstream

This checkout had no git history at all, so this one commit carries the whole
of the Everwood work as a single import on top of chairmanpow/benilla-octo's
`main` (706cd71). The two trees have genuinely diverged — each has files the
other does not — so this is a fork point, not a catch-up.

Today's work, which is the reason a baseline exists at all:

- Booth previews no longer cast world shadows (`NO_BOOTH_SHADOW`). Portrait
  characters were entering the sun's shadow cascades, so every skinned-rig
  shadow specialization compiled live mid-frame; the hitch detector logged
  "main thread blocked 1316 ms" beside a `compiled LIVE` warning. This was
  the Fashion/Tmog stutter.
- Per-pane dress-up: each `DressUpModel` pane assembles and stages its own
  tried-on look instead of every pane mirroring the live player.
- Item template cache is append-only JSONL written on the IO pool, replacing
  an 11.6 MB whole-map JSON rewrite on the main thread every 10 s.
- `WOW_SYSTEM_TIMING` rebuilt per-thread: it took 2 mutexes per system enter
  and 4 per exit, costing 15 ms a frame (590 fps -> 60) and corrupting the
  measurements it was taken to produce.
- The visibility-churn sweep moved to its own `WOW_FLASH_CHURN` switch, so a
  frame-cost reading no longer pays 2.7 ms a frame for it.

Local state (`benilla-config/`, `logs/`, `target/`) is excluded by the
existing .gitignore; the account credential it holds is not in this commit.

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

scripts/api-coverage.sh

@@ -50,9 +50,10 @@ awk -F'\t' -v ref="$REF" -v show_missing="$show_missing" -v show_beyond="$show_b
     if (o == "engine" || o == "lua") have++
     else if (o == "framexml") transcribable[$1] = 1
     else {
-      # Categorize the superset. Only the last bucket is an API-target question; the first is
-      # benilla being benilla, and the second is our Lua runtime being 5.1 where 1.12 is 5.0.
+      # Categorize the superset. Only the last bucket is an API-target question; the first two are
+      # benilla being benilla, and the third is our Lua runtime being 5.1 where 1.12 is 5.0.
       if ($1 ~ /^Benilla/)                                    bridge[$1] = 1
+      else if ($1 ~ /^__/)                                    internal[$1] = 1
       else if ($1 ~ /^(_G|_VERSION|coroutine|print|select)$/)  lua51[$1] = 1
       else                                                     api[$1] = 1
     }
@@ -65,7 +66,7 @@ awk -F'\t' -v ref="$REF" -v show_missing="$show_missing" -v show_beyond="$show_b
       n_ref["engine"] + n_ref["framexml"] + n_ref["lua"]
     printf "  engine    %5d functions, %5d other   <- benilla implements these in Rust\n", \
       n_ref_fn["engine"], n_ref["engine"] - n_ref_fn["engine"]
-    printf "  framexml  %5d functions, %5d other   <- the stock FrameXML defines these\n", \
+    printf "  framexml  %5d functions, %5d other   <- benilla transcribes these into assets/ui\n", \
       n_ref_fn["framexml"], n_ref["framexml"] - n_ref_fn["framexml"]
     printf "  lua       %5d functions, %5d other   <- mlua provides these\n", \
       n_ref_fn["lua"], n_ref["lua"] - n_ref_fn["lua"]
@@ -77,6 +78,7 @@ awk -F'\t' -v ref="$REF" -v show_missing="$show_missing" -v show_beyond="$show_b
 
     printf "\nbeyond 1.12, by kind — every one of these is a deliberate exception or a bug:\n"
     printf "  %3d  benilla host bridge      Benilla*, called only by our own FrameXML\n", length(bridge)
+    printf "  %3d  VM internals             __benilla_*, pushed by the tick\n", length(internal)
     printf "  %3d  Lua 5.1 past 1.12'\''s 5.0  ", length(lua51); dump(lua51, "")
     printf "  %3d  WoW API past 1.12        the phase-5 list\n", length(api)
     printf "  %3d  ours in Rust that 1.12 defines in FrameXML\n", length(transcribable)