feat(products): export hosted detail URL for fetched images; snapshot carries status (SD-0002 §6.5.5, INV-16)

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

backend/app/domains/products/service.py

@@ -12,7 +12,7 @@ from datetime import datetime, timezone
 
 import psycopg
 
-from app.platform import telemetry
+from app.platform import config, telemetry
 
 from . import codec, diff, repo, serialize, validate
 from .errors import (
@@ -242,7 +242,7 @@ def export_catalog(
         raise EmptyCatalog()
 
     def _stream() -> Iterator[str]:
-        yield from serialize.catalog_to_csv(snapshot)
+        yield from serialize.catalog_to_csv(snapshot, base_url=config.public_base_url())
         telemetry.emit(
             "catalog_exported",
             storefront_id=storefront_id,