build(core): regenerate the audio-fx runtime before the tests run

`src/generated/audio-fx-runtime-inline.ts` is what the engine injects into the
headless page to do the actual DSP, and nothing kept it in step with its
sources. Its sibling has `check:position-edits-render`, which rebuilds and then
`git diff --exit-code`s the artifact — but that form needs the file tracked, and
this one is gitignored.

Measured tonight while fixing the zero-frame guard: editing the stub and
re-running the engine's render tests injected the PREVIOUS bundle, so the fix
appeared not to work and the old DSP ran with nothing reporting the drift. That
is the exact preview/render divergence this stack exists to prevent, aimed at
whoever is developing it.

Making `test` regenerate it is the version of the gate that works without
touching .gitignore: the artifact cannot be stale when the tests read it.

Not covered: a fresh clone still cannot resolve `@hyperframes/core/audio-fx-runtime`
from `packages/engine` until core has been built at least once. CI survives on
build ordering. Tracking the artifact, or a pretest that builds core from the
engine, are both bigger calls than this one.

packages/core/package.json

@@ -549,7 +549,7 @@
   },
   "scripts": {
     "build": "bun run build:hyperframes-runtime && bun run build:position-edits-render && bun run build:audio-fx-runtime && tsc && tsx scripts/rewrite-esm-extensions.ts",
-    "test": "bun run check:position-edits-render && vitest run",
+    "test": "bun run check:position-edits-render && bun run build:audio-fx-runtime && vitest run",
     "test:watch": "vitest",
     "test:coverage": "vitest run --coverage",
     "test:runtime-coverage": "vitest run --coverage src/runtime",