Add historical chart of total voting weight over time

[Silver36-ship-it]

Closes #404

• Add getHistoricalWeightChangeEvents() to fetch all owner weight change events
• Add reconstructTotalWeightHistory() to reconstruct weight at each point in time
• Create HistoricalWeightChart component using Recharts
• Integrate chart into DashboardPage between GovernanceHealthWidget and Due Schedules
• Chart shows weight progression with loading, error, and empty states
• Supports sparse history and gracefully handles missing data

Summary

Type of Change

• Bug fix
• New feature
• Documentation
• Refactor

Related Issue

Closes #

Testing Checklist

• Existing tests pass locally
• New tests added to cover this change (where applicable)
• Manually verified the change works as expected
• Lint / type checks pass

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Add Historical Chart of Total Voting Weight Over Time

PR Description

This PR adds a time-series chart to the dashboard that visualizes how the multisig's total voting weight has changed over time. Owners can now see historical trends by examining weight changes reconstructed from on-chain events.

What's Changed

• New function getHistoricalWeightChangeEvents() in contract.ts

  • Fetches all available owner weight-change events from contract history (up to 100 events from last 10k ledgers)
  • Returns events sorted chronologically from oldest to newest
  • Gracefully handles fetch failures

• New function reconstructTotalWeightHistory() in contract.ts

  • Reconstructs total voting weight at each point in time from individual owner weight changes
  • Uses reported newTotalWeight when available; calculates deltas when not
  • Prevents negative weights with floor at 0
  • Returns array of WeightHistoryPoint objects with timestamp, ledger, totalWeight, and Date

• New type WeightHistoryPoint in contract.ts

  • Represents a single data point in weight history
  • Includes: timestamp (string), ledger (number), totalWeight (number), date (Date)

• New component HistoricalWeightChart in HistoricalWeightChart.tsx

  • React component using Recharts for visualization
  • Displays interactive line chart with green line showing weight progression
  • X-axis shows dates parsed from event timestamps
  • Y-axis shows total weight values
  • Includes loading, error, and empty states
  • Adds current total weight as final data point if different from last historical point
  • Shows event count and current weight metadata

• Updated DashboardPage in DashboardPage.tsx

  • Added import for HistoricalWeightChart
  • Integrated chart component between GovernanceHealthWidget and "Due Schedules" section
  • Passes currentTotalWeight and loading props

Why These Changes

The contract emits events for every owner weight change, providing a complete audit trail. This feature leverages that on-chain history to give owners visibility into how governance power has been distributed over time, enabling better financial oversight and trust.

Acceptance Criteria

• A chart shows how total voting weight has changed over time
• The series is derived from on-chain event history, not hard-coded values
• With little or no history, the chart shows a sensible empty or single-point state
• Chart gracefully handles missing data and sparse histories
• Loading and error states are properly handled
• Component integrates cleanly into existing dashboard layout

Testing

1. With history: Verify chart displays correctly when weight change events exist
2. Without history: Verify empty state message displays gracefully
3. Loading state: Verify loading spinner/message shows while fetching events
4. Error state: Verify error message displays if event fetch fails
5. Current weight: Verify current total weight is added as final data point
6. Responsive: Verify chart resizes correctly on different screen sizes

Dependencies

Requires installation of Recharts charting library:

npm install recharts

Technical Notes

• Events are fetched from last 10,000 ledgers (~1.4 hours of Stellar history)
• Timestamp parsing handles formatted dates like "Aug 31, 2026"
• X-axis labels intelligently sample events to avoid crowding (shows ~5 dates)
• Chart data includes both historical events and current state for complete picture
• All parsing errors are caught and logged without breaking the component

Related Issue

Closes dashboard analytics feature request for historical weight visibility.

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