Borrower role should not access dashboard (US-XA-004)

[andrewyager]

Description

Users in the Borrower group can currently log in and access the dashboard. The spec says Borrowers should only appear in checkout dropdowns, not have dashboard access.

Spec Sections: S10D (US-XA-004)
Severity: LOW
MoSCoW: SHOULD

What the spec requires

US-XA-004: Borrowers appear in checkout/transfer borrower dropdowns but are not full system users — they should not have dashboard access.

Xfail Test Coverage (1 test)

File	Test	Reason
test_cross_actor.py	TestUS_XA_004::test_borrower_user_cannot_log_in	Borrower not restricted from dashboard

Branch: feature/test-reorganisation-and-functional-suite (PR #37)