Describe the symbol scale in the project settings

Scene editing and Concepts explain the new Symbol scale field. Development has the e2e sum 1375.

Concepts.md

@@ -64,8 +64,9 @@ window, not of the space the row has left over — where play turns into a stop
 on, and pause into a second play sign while it is held. On the right stand the
 notice line, the save status, the frame rate and the **Account** menu. What the bar used to spell
 out lives in the menu now: the project list in *Open project…*, the project name, the
-**start-scene switch** (*Start scene* / *Active scene*, see **Start scene**) and the collision
+**start-scene switch** (*Start scene* / *Active scene*, see **Start scene**), the **symbol scale**
-layers in *Project settings…*. The active scene is picked where the scenes are — by double-clicking
+of the scene view's icons (see [Scene editing](Scene-editing)) and the collision layers in
+*Project settings…*. 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 types in
 two alphabetical groups, first what can be placed into a scene, then what only lives in the library
 (#43) — the line between them answers the question that follows right after "which type?".

Development.md

@@ -14,7 +14,7 @@ npm run build        # writes dist/ and regenerates index.html
 ./build.sh           # the same under `set -o pipefail`, for callers that pipe the output
 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)
-node tools/seed-e2e.mjs && node tools/e2e.mjs                 # 1374 editor checks, screenshots in /tmp/gm-e2e-*.png
+node tools/seed-e2e.mjs && node tools/e2e.mjs                 # 1375 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

Scene-editing.md

@@ -30,8 +30,10 @@ and particle source each show the same file in the Scene tab as in the Assets pa
 (`src/editor/panels/icons/`, drawn by `src/viewport/symbolIcons.ts`): **white, in a dark outline**,
 with no plate behind it, so every symbol reads the same on any ground. The outline is not a second
 file: `haloSvg` (`src/ui/svg.ts`) widens every shape of the icon by its stroke, and that silhouette
-is drawn dark under the icon. An icon is 18 world units across, stays upright and grows and shrinks
+is drawn dark under the icon. An icon is 18 world units across times the project's **Symbol scale**
-with the zoom like the scene. A file draws in its own units with the origin at its centre, and
+(**menu → Project settings…**, 0.1 to 4, default 1), stays upright and grows and shrinks with the
+zoom like the scene. The scale also sets the spacing of icons that share a spot and the outline of
+a selected behavior, container or rigidbody; a project of 16-pixel art may want 0.5. A file draws in its own units with the origin at its centre, and
 `currentColor` stands for the colour it is drawn in. Pixi's SVG parser is not a browser, so the
 files keep to what both draw alike, and `tests/ui/svg-icons.test.ts` holds them to it: only `path`,
 `circle`, `rect`, `ellipse` and `line` (Pixi reads `polygon` points as whole numbers), no