Visualize spending trends

[rappm]

Goal

Show spending pattern visualizations and trend charts over selectable time ranges.

Source

• FR-E2 in deliverables/PROBLEM_STATEMENT.md

Change

• Aggregate categorized spending over time.
• Render trend charts with selectable ranges.

Done When

• A user can select a time range.
• The UI shows spending trends for the selected range.
• Charts reflect imported and categorized transaction data.