[E09] Currency change notification modal

[IanMayo]

Epic

Part of E09: Provenance Graph

Problem

When currency checks detect that reference data has changed, the analyst must be informed and given control before any dependent calculations are re-run. External data changes can materially affect analytical conclusions, so this must be a blocking interaction.

Proposed Solution

A blocking modal that:

1. Lists all affected sources when currency checks complete
2. Provides per-source controls:
   • View diff — show old vs new value side-by-side before committing
   • Accept update — update the reference value at capture; trigger downstream recalculation
   • Reject update — retain existing value; suppress further alerts for this source in this session
3. Batches multiple changed sources into a single modal (avoids sequential interruptions on session open)
4. Tailored messages per currency state (changed, unavailable, source-structure-changed)

Success Criteria

• Modal blocks analyst interaction until all sources are acknowledged
• Multiple changed sources appear in a single modal with per-source controls
• View-diff shows old vs new values clearly
• Accept triggers downstream recalculation (via Unified activity panel #150)
• Reject suppresses further alerts for that source in the session
• Each currency state has a distinct visual indicator and message
• Accessible via keyboard (Enter/Space/Tab)

Dependencies

Requires #147 (session currency check orchestrator)

Complexity

High