fix(producer): shim CJS __dirname / __filename in ESM banner

[ukimsanov]

Summary

Bundled CJS deps — notably the ffmpeg/Emscripten wasm glue, which does scriptDirectory = __dirname + "/" — were crashing at render time with __dirname is not defined in ES module scope.

The existing banner shimmed require from import.meta.url but missed __dirname / __filename. Adds both globals alongside the existing createRequire shim.

Verification

• Verified by re-running a producer render after rebuild — ffmpeg pipeline completes cleanly
• node packages/producer/build.mjs esbuild bundles complete without errors

Sibling PRs in this stack

• fix(core/lint): findRootTag ignores <video>-like tokens inside HTML comments / <style> / <script> #1446 — fix(core/lint): findRootTag masks comment/style/script ranges
• feat(cli): capture-video on-demand fetcher + capture pipeline robustness #1447 — feat(cli): capture-video on-demand fetcher + capture pipeline robustness

All three independent; merge order doesn't matter.

Test plan

• bun run --filter @hyperframes/producer build passes
• Producer render of an existing project completes without __dirname errors

[ukimsanov]

Closing — verified the bug only fires when the producer is loaded via Node (Bun is permissive about __dirname in ESM scope). Internal team usage is Bun-first per CLAUDE.md + CI is on Bun, so no one currently hits it. Re-open if an external npx hyperframes user reports the crash from Node.