Describe empty asset groups and the add menu by heading (#361)

- Concepts explains the General settings switch that shows empty
  categories and types faint, and what a right-click on a category
  or type heading offers. It also names the "Create asset" title.
- Development counts 1906 checks.

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

Concepts.md

@@ -217,7 +217,8 @@ preset (see above), the **Link zoom** of the released game (see above), the **sy
 of the scene view's icons (see [Scene editing](Scene-editing)), the collision layers and the
 render layers in *Project settings…*. What is about the person at the screen rather than the
 project is in *General settings…* (#309), kept in this browser and the same in every project: the
-**zoom transition** (see below). A project is deleted in *Open project…*: **Delete** asks first, and Cancel, Esc
+**zoom transition** (see below) and whether the asset panel shows **empty categories and types**
+(see below). A project is deleted in *Open project…*: **Delete** asks first, and Cancel, Esc
 and the deletion itself all lead back to the project list. The active scene is picked where the scenes are — by double-clicking
 one in the **Assets** panel. The **Assets** panel's `+` creates an asset and opens its tab; its menu lists the categories of
 the panel (*Basics*, *Visuals*, *Logics*, *Physics*, *Audio*), and each opens a **submenu** beside it
@@ -227,8 +228,10 @@ category or on a click; moving on to another category swaps it after a short wai
 crossing the rows on its way into a submenu does not take it away. Picking a type closes both, and
 so do Escape and a click beside them. (Until then the menu was one list in two groups, placeable
 types and library ones, #43.)
-A right-click on a group heading or on the empty space below the rows opens the same menu (#244);
-a right-click on an asset keeps its own menu.
+A right-click on the empty space below the rows opens the same menu (#244). On a category heading
+it offers only the types of that category, without the submenu, and on a type heading only that
+type (#361). Each of these menus says *Create asset* in a muted line above its entries, so a
+click on a type reads as making one. A right-click on an asset keeps its own menu.
 Every type has an **icon** of its own, the same wherever the type shows: in the `+` menu, on the
 asset panel's groups, on a document's tab and at the end of a row in **Scene objects** (#176).
 The asset panel **groups by category and type** (#176). On top are the categories *Basics*,
@@ -240,6 +243,10 @@ category is **open** and every group **folded**; a click anywhere on a heading f
 and a heading is never selected. Selecting an asset from elsewhere (a picker, a graph, a new asset)
 unfolds its category and its group; folding the category or group the selected asset sits in lets
 go of the selection.
+With **Show empty asset categories and types** in *General settings…* (off by default, #361) the
+panel lists every category with every type, also those without assets. They stand faint, with a
+count of 0, and an empty type has no chevron, since there is nothing to unfold. A right-click on
+such a heading creates the first asset of that type.
 A click on a row only
 selects (the inspector shows it, no tab moves); a **double-click** opens the asset as a document
 in a tab of its own (see **The tab row**) — a behavior, state machine, shader, particles,

Development.md

@@ -19,7 +19,7 @@ php tests/php/accounts.test.php                               # the API's accoun
 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
 php tests/php/files.test.php                                  # uploaded files in a folder per account (#344), the same way
-node tools/seed-e2e.mjs && node tools/e2e.mjs                 # 1902 editor checks, screenshots in /tmp/gm-e2e-*.png
+node tools/seed-e2e.mjs && node tools/e2e.mjs                 # 1906 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