Describe Duplicate in the asset panel's right-click menu (#297)

- Concepts: the asset menu lists Duplicate, with where the copy
  lands, how it is named, and what keeps pointing at the original.
- Development: e2e total 1703.

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

Concepts.md

@@ -193,7 +193,12 @@ texture, animation, tile or container — and on a scene switches to the Scene t
 active one. `Enter` does the same once the list has keyboard focus (`Tab`).
 A sprite, camera, text or collider has no tab of its own, so a double-click on one does nothing.
 Right-clicking a row offers *Set as active scene*, *Set as start scene* / *Clear start scene*,
-*Create sprite from texture*, *Create animation from texture* and *Delete…*. In
+*Create sprite from texture*, *Create animation from texture*, *Duplicate* and *Delete…*.
+*Duplicate* puts a copy right below the original, named the way a new asset would be ("Crate 2"),
+selects it and opens its tab where it has one (a copied scene does not become the active one);
+one undo takes it out again. The copy has its own values, graph,
+frames and objects, so editing it leaves the original alone. Whatever pointed at the original
+(a sprite wearing it, an animation's root, a placed object) keeps pointing at the original. In
 **Scene objects** it offers *Select asset*, *Open asset* (the same as double-clicking the asset
 in the asset panel; greyed out for a kind that has no editor of its own, such as a sprite or a
 camera), *Add collider…*, *Add rigidbody…* and *Add joint…* (each opens a searchable menu: a new one

Development.md

@@ -18,7 +18,7 @@ php tests/php/accounts.test.php                               # the API's accoun
                                                               #   has and the web server's container has not (SKIP there)
 php tests/php/snapshots.test.php                              # the snapshot store (#231), the same way
 php tests/php/releases.test.php                               # the release store (#266), the same way
-node tools/seed-e2e.mjs && node tools/e2e.mjs                 # 1701 editor checks, screenshots in /tmp/gm-e2e-*.png
+node tools/seed-e2e.mjs && node tools/e2e.mjs                 # 1703 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