fix: add pitcher_id null guard and remove unrelated Dockerfile changes

- Mirror the batter_id is None guard in _build_pitching_groups() so that
  a StratPlay row with a null pitcher_id is skipped rather than creating
  a None key in the groups dict (which would fail on the NOT NULL FK
  constraint during upsert).
- Revert Dockerfile to the next-release base: drop the COPY path change
  and CMD addition that were already merged in PR #101 and are unrelated
  to the ProcessedGame ledger feature.

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

Dockerfile

@@ -7,6 +7,4 @@ RUN pip install --no-cache-dir -r requirements.txt
 RUN playwright install chromium
 RUN playwright install-deps chromium
 
-COPY ./app /usr/src/app/app
-
-CMD ["uvicorn", "app.main:app", "--host", "0.0.0.0", "--port", "80"]
+COPY ./app /app/app

app/services/season_stats.py

@@ -159,6 +159,10 @@ def _build_pitching_groups(plays):
     for play in plays:
         pitcher_id = play.pitcher_id
         pitcher_team_id = play.pitcher_team_id
+
+        if pitcher_id is None:
+            continue
+
         key = (pitcher_id, pitcher_team_id)
         g = groups[key]