Derive cumulative totals from yearly atom totals (no DB storage)

[Gorm2303]

Given cumulative totals exist in the taxonomy (deposited, withdrawn, taxed, fees, returned)
When the frontend requests totals/phase totals for a Tier 1 run
Then the backend derives cumulative totals by cumulatively summing the stored yearly totals (per percentile series)

Acceptance criteria

deposited_to_date = Σ deposit_year

withdrawn_to_date = Σ withdraw_year

taxed_to_date = Σ tax_year

fees_to_date = Σ fee_year

returned_to_date = Σ return_year

Derived totals are documented as COMPUTED

No new cumulative totals are persisted in DB