Describe loading every picture ahead

Textures gets a paragraph on the preload: every picture, font and
pixel art cel of the project is requested when it opens or changes.
Development moves the check count to 1423.

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

Development.md

@@ -15,7 +15,7 @@ npm run build        # writes dist/ and regenerates index.html
 php tools/make-user.php <name> <password> [admin|user]        # an account; every tool signs in (see Accounts)
 php tests/php/accounts.test.php                               # the API's account rules, no server needed (CI's gate job)
 php tests/php/snapshots.test.php                              # the snapshot store (#231), the same way
-node tools/seed-e2e.mjs && node tools/e2e.mjs                 # 1422 editor checks, screenshots in /tmp/gm-e2e-*.png
+node tools/seed-e2e.mjs && node tools/e2e.mjs                 # 1423 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

Textures.md

@@ -209,6 +209,11 @@ to the sheet itself.
 **Nothing ever breaks on a missing picture.** While an image loads, and for a reference that
 dangles because the texture was deleted, the sprite draws its plain colour — exactly what it
 looked like before textures existed. So there is no placeholder, no flicker and no error path.
+
+**Every picture is loaded ahead.** As soon as a project is opened, and whenever an asset is
+added, the editor fetches every image, font and pixel art cel the project names, used or not.
+Nothing waits for its first draw: an animation or an animated tile that reaches a frame from a
+picture of its own would otherwise blink out once, the first time it gets there.
 Deleting a texture warns how many sprites reference it (a texture is never *placed*, so
 counting placed instances would report "unused" for a picture a dozen sprites are showing).