refactor(parsers): single shared FFmpeg/FFprobe binary resolver

The cli, engine, and lint packages each carried their own copy of the
ffmpeg/ffprobe lookup, annotated fallow-ignore code-duplication, and the
copies had drifted: the engine copy handled Windows PATHEXT and executed
which/where without a shell but lacked the Homebrew-dirs fallback for
GUI-spawned processes; the cli copy had the opposite. One resolver in
@hyperframes/parsers (the dependency-graph bottom) now carries the union
of both hardenings, and all three packages delegate to it. Every
consumer gets strictly more robust resolution; env-override semantics
per call site are preserved via configuredMustExist.

packages/parsers/tsup.config.ts

@@ -15,6 +15,7 @@ export default defineConfig({
     composition: "src/composition.ts",
     compositionContract: "src/compositionContract.ts",
     subCompositionValidity: "src/subCompositionValidity.ts",
+    ffBinaries: "src/ffBinaries.ts",
   },
   format: ["esm"],
   outDir: "dist",