feat: schedule S3 upload for variant cards after Playwright render

Adds BackgroundTasks to the card render endpoint. After rendering a
variant card (variant > 0) where image_url is None, schedules
backfill_variant_image_url to upload the PNG to S3 and populate
image_url on the card row.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

app/routers_v2/players.py

@@ -2,7 +2,15 @@ import datetime
 import os.path
 
 import pandas as pd
-from fastapi import APIRouter, Depends, HTTPException, Request, Response, Query
+from fastapi import (
+    APIRouter,
+    BackgroundTasks,
+    Depends,
+    HTTPException,
+    Request,
+    Response,
+    Query,
+)
 from fastapi.responses import FileResponse
 from fastapi.templating import Jinja2Templates
 from typing import Optional, List, Literal
@@ -732,6 +740,7 @@ async def get_one_player(player_id: int, csv: Optional[bool] = False):
 @router.get("/{player_id}/{card_type}card/{d}/{variant}")
 async def get_batter_card(
     request: Request,
+    background_tasks: BackgroundTasks,
     player_id: int,
     card_type: Literal["batting", "pitching"],
     variant: int = 0,
@@ -906,6 +915,27 @@ async def get_batter_card(
     #     save_as=f'{player_id}-{d}-v{variant}.png'
     # )
 
+    # Schedule S3 upload for variant cards that don't have an image_url yet
+    if variant > 0 and tier is None:
+        CardModel = BattingCard if card_type == "batting" else PitchingCard
+        try:
+            card_row = CardModel.get(
+                (CardModel.player_id == player_id) & (CardModel.variant == variant)
+            )
+            if card_row.image_url is None:
+                from app.services.card_storage import backfill_variant_image_url
+
+                background_tasks.add_task(
+                    backfill_variant_image_url,
+                    player_id=player_id,
+                    variant=variant,
+                    card_type=card_type,
+                    cardset_id=this_player.cardset.id,
+                    png_path=file_path,
+                )
+        except CardModel.DoesNotExist:
+            pass
+
     return FileResponse(path=file_path, media_type="image/png", headers=headers)