Time-debt ledgers: anchor known balances, sum only positive debt

When a user gives a known balance for a past day, for example 'I was 20 h ahead on Oct 25', store it as a per-goal anchor {day: balance}. The replay sets the balance at the end of that day. Do not move the seed date: a moved seed hides all history before it. To let credit (a negative balance) bank, remove the max(0, ...) floor only from a fixed start date, so older rows still match the stored ledger. Make the cross-goal total sum max(0, owed) for each goal, or one goal's credit will hide another goal's debt. To excuse a span of days, a dated 'Paused' entry in the goal's status history is simpler than new code, if the target already applies only on Active days.