Free a redrawn picture only once no shader names it (#293)

Editing a vector drawing made Pixi warn "destroyed while still bound
to a shader", twice with every change, once it had begun. It began
where an object wears the drawing through a shader asset. Each
change draws the picture anew and destroyed the one before it, but
the mesh of that object keeps its picture bound until it syncs. The
issue also asks for the button "Add shape" to go: a shape without
points cannot be given any, the Pen draws a new one.

- GeneratedPictures takes two more callbacks. inUse says that a
  picture cannot be freed yet, soon runs a retry once whoever asked
  is done.
- A replaced picture that is still in use waits in a list of its
  own. It is freed right after the redraw that asked, as a rule. On
  a later ask where its wearer was not part of that redraw.
- TextureLibrary tells a bound picture by the listeners for change
  on its source. Under WebGL the bind groups are the only ones that
  listen there. The retry is a microtask.
- The rule is asked for every drawn picture alike, whoever wears it.
- The inspector of a drawing and of a shape has no "Add shape" any
  more. "Delete shapes" for several selected shapes stays.

Decided here:

- Under the list of shapes a second note says "The Pen draws a new
  shape." while only the asset is selected.

Found on the way:

- Reproduced on a throwaway copy of the project the report came
  from: 6 warnings for 3 changes with the shader override on the
  object, none without it. After the change none, and no replaced
  picture is left waiting.
- The fixture project of the tests never showed the warning. No
  object there wore a drawing through a shader.

Tests:
- Gate on melektaus-atx: 211 files, 3219 tests (3209 + 10), exit 0
- e2e 47,48 on melektaus-atx: 113 checks, all pass
- e2e 28,30,31,39,40,47,48: 350 checks, all pass, run before the
  wording of the new note changed
- The first gate was red: an existing test read the wording of the
  note that had changed. Only three test files had been run after
  the change.
- No full run and no smokes. The sum of 1668 (1667 + 1) is reckoned,
  1667 is what CI counted for ec2fd90.
- Ten unit tests, five of them against the real bind group of Pixi
  in tests/viewport/bound-pictures.test.ts
- One e2e check in block 47b-ii of module 47: a drawing worn through
  a shader, three changes, no warning. The check on "Add shape" now
  reads that there is no such button.
- Nine unit counter-probes and two browser counter-probes all fail
  their tests. Without the change the new check counts 6 warnings.
- Not checked: a tilemap or a particle emitter holding a picture
  bound the same way. Nothing was looked at after the build, the
  new note included.

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

README.md

@@ -45,7 +45,7 @@ npm run build        # writes dist/ and regenerates index.html; the folder is wh
 The browser suite and the three example games need a machine with a GPU:
 
 ```bash
-node tools/seed-e2e.mjs && node tools/e2e.mjs      # the editor, 1667 checks (GM_STEPS=20 for one step)
+node tools/seed-e2e.mjs && node tools/e2e.mjs      # the editor, 1668 checks (GM_STEPS=20 for one step)
                                                    #   every tool signs in first – see the Accounts page
 node tools/seed-jumprun.mjs && node tools/smoke-jumprun.mjs
 node tools/seed-tetris.mjs && node tools/smoke-tetris.mjs