Native bank statement import — feature contribution (PR #66)

Hi everyone,

I've been building a native bank statement import feature for FrontAccounting and
would love some feedback from the core team. It's submitted as a GitHub pull request
against the mirror repo, so the code is all there to review:

  Pull request: [github.com/FrontAccountingERP/FA/pull/66]
  Fork:        [github.com/Xarrathh/FA  (branch: bank-statement-import)]

What it does
- Imports a fixed-format CSV (Date, Description, Debit, Credit) straight into the
  General Ledger, no pre-formatting with account codes.
- Auto-allocates recurring payees via rules you define (description -> GL account,
  with payment / deposit / either direction).
- Manual review step for unmatched rows.
- Optional VAT split per line (net + VAT to the company's VAT account).
- Mandatory "I have made a backup" confirmation before posting.
- Per-row error reporting instead of an opaque count.
- Rules can be exported/imported as CSV between companies.

It's a native core feature (Banking & General Ledger menu), not an extension, and
sits alongside the existing import_transactions extension as a simpler alternative
for raw bank statements.

How to test
1. Log in as System Administrator.
2. Banking & General Ledger -> Bank Statement Import.
3. Upload a CSV with the header: Date, Description, Debit, Credit.
4. Parse, review, tick the backup confirmation, then Import.

Tested against 2.4.20. Happy to adjust anything the team wants changed.

Author: Pierre-Johan Goosen, with the assistance of Hermes Agent (AI).