feat(ingest): source-bucket registry keyed on ingest source

Generalises the Daedalus-only cross-bucket fetch into a registry
(SOURCE_S3_BUCKETS) keyed on the IngestJob `source` field, so new
upstream sources (Spelunker) can ingest from their own buckets. The
ingest task now calls fetch_from_source(job.source, job.s3_key) and
falls back to "daedalus" for blank/unknown sources (backwards compatible).

Adds SPELUNKER_S3_* env vars and worker env scoping. Replaces
daedalus_s3.py with source_s3.py.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

docker-compose.yaml

@@ -339,6 +339,13 @@ services:
       - DAEDALUS_S3_REGION_NAME=${DAEDALUS_S3_REGION_NAME}
       - DAEDALUS_S3_USE_SSL=${DAEDALUS_S3_USE_SSL}
       - DAEDALUS_S3_VERIFY=${DAEDALUS_S3_VERIFY}
+      - SPELUNKER_S3_ENDPOINT_URL=${SPELUNKER_S3_ENDPOINT_URL}
+      - SPELUNKER_S3_ACCESS_KEY_ID=${SPELUNKER_S3_ACCESS_KEY_ID}
+      - SPELUNKER_S3_SECRET_ACCESS_KEY=${SPELUNKER_S3_SECRET_ACCESS_KEY}
+      - SPELUNKER_S3_BUCKET_NAME=${SPELUNKER_S3_BUCKET_NAME}
+      - SPELUNKER_S3_REGION_NAME=${SPELUNKER_S3_REGION_NAME}
+      - SPELUNKER_S3_USE_SSL=${SPELUNKER_S3_USE_SSL}
+      - SPELUNKER_S3_VERIFY=${SPELUNKER_S3_VERIFY}
       # Celery / RabbitMQ
       - CELERY_BROKER_URL=${CELERY_BROKER_URL}
       - CELERY_RESULT_BACKEND=${CELERY_RESULT_BACKEND}