fix: replace model_validate(..., update=) with .model_copy(update=)

Pydantic v2 model_validate() does not accept an update kwarg; the correct
pattern is model_validate(obj).model_copy(update={...}).

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

api/src/rehearsalhub/routers/sessions.py

@@ -34,7 +34,7 @@ async def list_sessions(
     repo = RehearsalSessionRepository(session)
     rows = await repo.list_for_band(band_id)
     return [
-        RehearsalSessionRead.model_validate(s, update={"recording_count": count})
+        RehearsalSessionRead.model_validate(s).model_copy(update={"recording_count": count})
         for s, count in rows
     ]
 
@@ -58,7 +58,7 @@ async def get_session_detail(
         raise HTTPException(status_code=status.HTTP_404_NOT_FOUND, detail="Session not found")
 
     songs = [
-        SongRead.model_validate(s, update={"version_count": len(s.versions)})
+        SongRead.model_validate(s).model_copy(update={"version_count": len(s.versions)})
         for s in rehearsal.songs
     ]
     return RehearsalSessionDetail.model_validate(
@@ -89,4 +89,4 @@ async def update_session(
     if updates:
         rehearsal = await repo.update(rehearsal, **updates)
 
-    return RehearsalSessionRead.model_validate(rehearsal, update={"recording_count": 0})
+    return RehearsalSessionRead.model_validate(rehearsal).model_copy(update={"recording_count": 0})

api/src/rehearsalhub/routers/songs.py

@@ -83,7 +83,7 @@ async def search_songs(
         unattributed=unattributed,
     )
     return [
-        SongRead.model_validate(s, update={"version_count": len(s.versions)})
+        SongRead.model_validate(s).model_copy(update={"version_count": len(s.versions)})
         for s in songs
     ]
 
@@ -110,7 +110,7 @@ async def update_song(
     if updates:
         song = await song_repo.update(song, **updates)
 
-    return SongRead.model_validate(song, update={"version_count": len(song.versions)})
+    return SongRead.model_validate(song).model_copy(update={"version_count": len(song.versions)})
 
 
 @router.post("/bands/{band_id}/songs", response_model=SongRead, status_code=status.HTTP_201_CREATED)

api/src/rehearsalhub/services/nc_scan.py

@@ -187,7 +187,7 @@ async def scan_band_folder(
         )
 
         imported += 1
-        read = SongRead.model_validate(song, update={"version_count": 1, "session_id": rehearsal_session_id})
+        read = SongRead.model_validate(song).model_copy(update={"version_count": 1, "session_id": rehearsal_session_id})
         yield {"type": "song", "song": read.model_dump(mode="json"), "is_new": is_new}
 
     yield {