Add Siemens CT document evaluation scenario (three-step pipeline)

- scenarios/siemens_build/siemens-pdf-build.yaml: dataset build for all 17
  Siemens medical-imaging PDFs (aliyun_docmind parser, 10 questions/doc,
  failure_mode=skip, ~170 question total)
- scenarios/offline/siemens-pdf-offline-smoke.yaml: offline evaluation using
  source chunks as contexts and ground_truth as answer (up to 30 samples)
- scenarios/online/siemens-pdf-question-bank-online.yaml: online evaluation
  calling siemens_pdf_qa adapter, batch_size=4, up to 50 samples
- apps/siemens_pdf_qa/adapter.py: Siemens-specific adapter with bilingual
  (zh/en) system prompt and strict evidence-grounding for CT domain
- scripts/build_siemens_offline_smoke.py: helper to derive offline smoke CSV
  from completed dataset build artifacts (run after dataset build step)
- docs/superpowers/specs/2026-06-15-siemens-scenario-design.md: design spec

All three scenarios are automatically discovered by the web console.

Co-Authored-By: Claude Sonnet 4 <noreply@anthropic.com>

scenarios/siemens_build/siemens-pdf-build.yaml

@@ -0,0 +1,17 @@
+job_name: siemens-pdf-question-bank
+input:
+  path: ../../datasets/siemens-pdfs
+  glob: "*.pdf"
+parser:
+  provider: aliyun_docmind
+  failure_mode: skip
+generation:
+  output_type: online_question_bank
+  review_mode: draft_with_manual_review
+  max_questions_per_document: 10
+  max_source_chunks_per_question: 3
+output:
+  dataset_path: ../../datasets/raw/generated/siemens-pdf-question-bank.csv
+  artifact_dir: ../../outputs/dataset-builds/siemens-pdf-question-bank
+runtime:
+  max_documents: 17