Say the editor loads no bold face and why the test checks it (#273)

- Architecture: Source Sans 3 in 400, 500 and 600.
- Development: the font test holds the loaded weights to the
  fontWeight settings in src/ both ways.

Architecture.md

@@ -123,7 +123,7 @@ src/runtime/physics/   engine (loads Rapier once, reports its state, converts be
                        without the engine), bodyGeometry (a world shape as the engine colliders of a body, and the
                        poses handed between the two)
 src/ui/                widget toolkit (generic, knows nothing about assets); fonts (the faces the editor ships:
-                       Source Sans 3 in 400, 500, 600 and 700, Source Code Pro 400, Latin only, #202/#214), icons +
+                       Source Sans 3 in 400, 500 and 600, Source Code Pro 400, Latin only, #202/#214/#273), icons +
                        Icon (the menu's tick boxes and current-entry dot as SVG files, and a widget that shows one file
                        on its own: a symbol the Latin subset lacks is never written as a character, #214); SortableList + sortable (the layer list of every editor that has one: rows dragged into order, eye, duplicate, cross, rename in place; the index arithmetic of a list shown upside down, kept apart so it is measured without a canvas)
 src/viewport/          WorldViewport (the drawing of a world or a holder, the base of every view; it draws from

Development.md

@@ -136,7 +136,9 @@ such picture on screen as `{ x, y, menu }`: `menu` says whether the button it si
 In a step, `t.findIcon(id, menu)` and `t.clickIcon(id, menu)` do the same as `find` and `clickText`.
 A menu's tick boxes are read through `t.menuTicked()` as `{ label, ticked }`. The unit test
 `tests/ui/fonts.test.ts` reads the character map straight out of the font files and fails on any
-character in `src/` that one of the shipped faces lacks.
+character in `src/` that one of the shipped faces lacks. It also holds the loaded weights to
+the `fontWeight` settings in `src/`, both ways: a weight the editor sets needs its face, and a face
+no one sets fails as well, since the editor waits for every face before it starts (#273).
 
 **Many pixels are one read, not many.** Every `__gm.pixelAt` renders the stage into a render
 texture of its own and waits for the GPU to hand the pixel back: about 2 ms here, about 7 ms