[Maintenance] Transaction table rewrite

### Verified feature request does not already exist?

- [X] I have searched and found no existing issue

### 💻

- [ ] Would you like to implement this feature?

### Pitch: what problem are you trying to solve?

See more information here:

https://github.com/actualbudget/actual/blob/40a23f326341b665298561f4dbd8b4d8296e3365/CONTRIBUTING.md#rewriting-the-transaction-table

### Describe your ideal solution to this problem

_No response_

### Teaching and learning

_No response_

Start with the linked CONTRIBUTING.md section, “rewriting the transaction table,” which is the issue’s only implementation guidance. Use that section to determine the rewrite’s scope; done means completing the documented transaction-table work and validating the affected behavior.

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