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>

biome.json

@@ -38,16 +38,6 @@
           }
         }
       }
-    },
-    {
-      "includes": ["examples/**/*.ts", "packages/workflow/__tests__/fixtures/**/*.ts"],
-      "linter": {
-        "rules": {
-          "style": {
-            "noDefaultExport": "off"
-          }
-        }
-      }
     }
   ],
   "linter": {