feat(immich): write-back (upsert_tag, tag_assets) + _pipeline tag conventions

shared/photoflow/immich/pipeline.py

@@ -0,0 +1,11 @@
+ROOT = "_pipeline"
+PROCESSED = f"{ROOT}/processed"
+NON_TRIP = f"{ROOT}/non-trip"
+
+
+def ai_rating(n: int) -> str:
+    return f"{ROOT}/ai-rating/{n}"
+
+
+def is_pipeline_tag(name: str) -> bool:
+    return name == ROOT or name.startswith(ROOT + "/")