Preserve fixed charges when refreshing drafts

[lago-claude-ai-agent]

Draft refresh now rebuilds pay-in-advance fixed charges from their full event history and deducts same-period amounts invoiced separately, preserving the original full-period charge after an immediate units increase.

The refresh adds one indexed aggregate fee query per pay-in-advance fixed charge and does not add event loops or jobs.

[lago-claude-ai-agent]

HOLD: The refreshed fee double-counts paid units after an immediate increase.

• Keep the rebuilt fee's paid-unit ledger from including units already represented by the separate delta fee; after 10 → 12 and refresh, the retained fees currently sum to 14 paid units, so a subsequent increase to 13 is not billed.
• Add a regression covering another immediate increase after refresh and assert that its delta is invoiced.

[lago-claude-ai-agent]

• Proration and reconciliation: pinned the day-nine two-unit increase while refresh rebuilds from fixed-charge events and deducts the separately invoiced amount.

[lago-claude-ai-agent]

HOLD: Refresh double-counts paid units after an immediate fixed-charge increase.

• Keep the refreshed draft fee's billed units from including the units represented by the separate delta fee; after 10 → 12, the persisted fees total 14 units, so a later increase to 13 is incorrectly billed as zero.
• Add a regression for another immediate increase after refresh and assert that the new delta is invoiced.