refactor: named exports (run + descriptor), remove build pipeline

- Bundle contract: export const run + export const descriptor (no default export)
- add only accepts .esm.js, extracts descriptor via dynamic import → .yaml
- Removed: build-pipeline, generate-types, json-schema-to-ts
- Worker loads mod.run instead of mod.default
- Biome: no more noDefaultExport overrides for bundles
- 62 tests pass, biome clean

Closes #8
小橘 <xiaoju@shazhou.work>

examples/hello-world.ts

@@ -23,7 +23,7 @@ const greeter: Role<Roles["greeter"]> = async (ctx) => ({
   meta: { greeting: "Hello!" },
 });
 
-export default createRoleModerator<Roles>({
+export const run = createRoleModerator<Roles>({
   roles: { greeter },
   moderator(ctx) {
     return ctx.steps.length === 0 ? "greeter" : END;