Properties node: name each shader param by its shader (#66)

The + Property menu of the Properties node offered every shader's params
for every sprite. Each shader row now carries its shader name, and a name
shared by two shaders lists both: "brightness (Adjust colors, Neon glow)".
Sprite-owned rows stay unlabelled.

The note hangs off a map keyed by the def object, not by the name -- a
sprite property and a shader param may share a name (#63), and keying by
name would label the wrong row.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

README.md

@@ -37,7 +37,7 @@ 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, 725 checks (GM_STEPS=20 for one step)
+node tools/seed-e2e.mjs && node tools/e2e.mjs      # the editor, 727 checks (GM_STEPS=20 for one step)
 node tools/seed-jumprun.mjs && node tools/smoke-jumprun.mjs
 node tools/seed-tetris.mjs && node tools/smoke-tetris.mjs
 node tools/seed-actor.mjs && node tools/smoke-actor.mjs