embedding-worker CJS ESM location

Resolve local embedding-worker entrypoints according to module system: use __filename in CommonJS and import.meta.url in ESM. Preserve the source/build shim that keeps the CommonJS branch valid; a unified mechanism fails because import.meta.url needs a CJS shim while __filename is unavailable in native ESM. Handle development .ts execution under tools such as Vitest or tsx separately from production worker sources.