Payment history was missing

I imported a loan I'd been paying on for months, and the payments I'd already made simply didn't exist — no history, and no way to add them.

That's the normal case, not the edge case. Nobody starts tracking a loan the day they open it. Builds 5 and 6 filled the gap:

• A history screen per account: paid-so-far on top, still-owed below.
• Log a past payment — and after I caught the first version getting this backwards, logging a payment now reduces the balance by default, with a toggle for the exceptions.
• Backfill for the other case: the balance was already correct, and I just wanted the record to show the installments I'd paid. History only, balance untouched.

The difference between those last two matters more than it looks — one changes what you owe, the other changes what the record shows. Collapsing them was the first version's mistake.