Animations: scroll the timeline rows up and down (#413)

- Animations: the wheel over the header column scrolls the rows, the
  ruler stays put, a scrollbar at the right edge can be dragged. A
  picked or added row out of view is scrolled into it. The middle
  button now pans both ways.
- Development: 2059 editor checks.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

Animations.md

@@ -127,7 +127,10 @@ the removed frames and pulls the rest earlier. Each is one undo step. The same m
 *Delete row* for the row under the pointer; right-clicking a row's header also picks that row. On a
 *Video time* row it also offers to key the video at 1x to its end (see [Videos](Videos)). Click or drag the ruler to scrub. The wheel zooms the
 frames about the pointer, from 48 pixels a frame out to 50 frames a pixel, so an hour at 30 fps
-fits a screen (#407). `Shift`+wheel scrolls, the middle button (or `Shift`+drag) pans. Groups cannot be collapsed yet.
+fits a screen (#407). `Shift`+wheel scrolls across, `Shift`+drag pans across, the middle button
+pans both ways. **More rows than room** (#413): the wheel over the header column scrolls the rows
+up and down, the ruler stays where it is, and a scrollbar at the right edge can be dragged. A row
+picked or added out of view is scrolled into it. Groups cannot be collapsed yet.
 Scrubbing while the animation plays pauses it, and the button turns back to *Play*.
 
 **Play, stop, pause.** `Play animation` starts an animation on an object (both are ports: the

Development.md

@@ -21,7 +21,7 @@ php tests/php/releases.test.php                               # the release stor
 php tests/php/files.test.php                                  # uploaded files in a folder per account (#344), the same way
 php tests/php/videos.test.php                                 # the video store, its queue and the worker (#402), with the
                                                               #   real ffmpeg: the CI image and game-maker-video have it
-node tools/seed-e2e.mjs && node tools/e2e.mjs                 # 2057 editor checks, screenshots in /tmp/gm-e2e-*.png
+node tools/seed-e2e.mjs && node tools/e2e.mjs                 # 2059 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