Bug in Processing-step slider

[suung]

Bug in Processing-step slider
Branch: feature/processing-steps-slider
Background
Analysts need Chunk / Embed / Map / Answer without always running full LLM answer.
Goals

• Slider + early stop; Chunk/Embed work even with questions selected; chunk-only All Results.
  Acceptance criteria
• Chunk/Embed stop before Map/Answer
• Questions selected does not bypass partial steps
• Cached chunks shown after partial run
• Chunk-only reports appear in All Results
• tests/test_processing_steps.py green