Left column splitter in Concepts, check total 1009

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

Concepts.md

@@ -52,6 +52,9 @@ Right-clicking a row offers *Set as active scene*, *Set as start scene* / *Clear
 *Create sprite from texture*, *Create animation from texture* and *Delete…*. In
 **Scene objects** it offers *Select asset*, *Add collider*, *Create container*, *Unpack
 container*, *Unparent*, *Expand all* / *Collapse all* and *Remove*.
+The asset panel and **Scene objects** share the left column; the divider between them drags
+the height from one to the other, and dragged all the way either keeps its header. The split is a
+share of the column, so a taller or shorter window keeps it.
 
 **The tab row.** The centre column carries one button per tab. When the column is too narrow to
 hold them all — a small window, or the side panels dragged wide — the ones that do not fit move

Development.md

@@ -12,7 +12,7 @@ npm run check        # typecheck + lint + format:check + tests, the gate CI runs
                      #   code is lost (tail's is reported), so a red run reads as green
 npm run build        # writes dist/ and regenerates index.html
 ./build.sh           # the same under `set -o pipefail`, for callers that pipe the output
-node tools/seed-e2e.mjs && node tools/e2e.mjs                 # 1006 editor checks, screenshots in /tmp/gm-e2e-*.png
+node tools/seed-e2e.mjs && node tools/e2e.mjs                 # 1009 editor checks, screenshots in /tmp/gm-e2e-*.png
 GM_STEPS=20 node tools/e2e.mjs                                # or 1-12, or 6,20 — a subset while working on one step
 ./e2e.sh start [GM_STEPS]                                     # the same run detached, see below
 ./e2e.sh status                                               # live progress, or the last run's result
@@ -232,4 +232,4 @@ widths to find click points. The **render device is not in this repo** — `/dev
 and a 1 GB `/dev/shm` come from `container.options` in the runner's own `config.yaml`, which
 applies to every job on that runner. Without them chromium falls back to llvmpipe, which gets
 WebGL 1.0 only. Measured in the job container: `ANGLE (Intel, Vulkan 1.3.230, HD Graphics 630)`,
-WebGL 2.0, and the same 1006 checks as here.
+WebGL 2.0, and the same 1009 checks as here.