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

shared/photoflow/immich/client.py

@@ -72,3 +72,22 @@ class ImmichClient:
                              timeout=self.timeout)
         r.raise_for_status()
         return r.content
+
+    def upsert_tag(self, name: str) -> str:
+        r = self.session.put(self._url("/api/tags"),
+                             json={"tags": [name]}, timeout=self.timeout)
+        r.raise_for_status()
+        for tag in r.json():
+            if tag.get("value") == name or tag.get("name") == name:
+                return tag["id"]
+        resolved = self.resolve_tag_id(name)
+        if resolved is None:
+            raise RuntimeError(f"upsert_tag: could not resolve id for {name!r}")
+        return resolved
+
+    def tag_assets(self, tag_id: str, asset_ids: list[str]) -> None:
+        if not asset_ids:
+            return
+        r = self.session.put(self._url(f"/api/tags/{tag_id}/assets"),
+                             json={"ids": asset_ids}, timeout=self.timeout)
+        r.raise_for_status()