Add opt-in season cascade to series ingestion

Ingesting a series only ever produced season stubs -- getting actual
episodes meant calling POST /admin/ingest/season once per season by
hand, which is exactly what manual end-to-end testing kept requiring
for every multi-season show.

POST /api/v1/admin/ingest/series now takes include_seasons (default
false, since a show can have dozens of seasons and that's dozens of
TMDb calls fired from one request). When true, ingest_series_task
fans out one ingest_season job per season once the series succeeds,
using arq's own ctx['redis'] connection for the job (the same pattern
arq's docs recommend for job chaining) rather than a second unrelated
connection. Each fanned-out season job still goes through
get_or_create_ingestion_job, so re-running a cascaded series ingestion
reuses the same season job rows instead of creating duplicates.

Co-Authored-By: Claude Sonnet 5 <[email protected]>

app/services/ingestion/runner.py

@@ -25,6 +25,7 @@ from app.repositories.provider_repository import (
     mark_job_running,
     mark_job_succeeded,
 )
+from app.repositories.tv_repository import get_seasons_for_series
 from app.services.ingestion.movie_ingestion import ingest_movie
 from app.services.ingestion.person_ingestion import ingest_person
 from app.services.ingestion.series_ingestion import ingest_season, ingest_series
@@ -138,3 +139,14 @@ async def run_season_ingestion(
             session, provider, series_external_id, season_number, ingestion_job_id=job_id
         ),
     )
+
+
+async def get_series_season_numbers(series_id: uuid.UUID) -> list[int]:
+    """All season numbers a just-ingested series has, for cascading into
+    per-season ingestion jobs (see `app/workers/tasks.py:ingest_series_task`,
+    `include_seasons`). A short-lived session of its own since this runs
+    after `run_series_ingestion`'s own session has already closed."""
+
+    async with session_scope() as session:
+        seasons = await get_seasons_for_series(session, series_id)
+        return [season.season_number for season in seasons]