Add per-indicator contribution breakdown

[PawanRamaMali]

Summary

When a pillar score is low, users need to know which specific indicators are dragging it down to prioritize remediation.

Tasks

• Add indicator_contributions() function returning each indicator's contribution to its pillar score
• Rank indicators by impact (highest remediation value first)
• Add "what-if" analysis: if indicator X improved to score Y, what would the new pillar score be?
• Include actionable remediation suggestions per indicator (e.g., "Q-DEFINE-001: Add dataset labels to Define-XML")

Why

SCI is useful for the go/no-go decision. Indicator contributions are useful for the "what do we fix first?" decision.