feat: Add CD001-MCP FinStripe Repository Coverage Tests (CD001, #27)

[steadhac]

PR #313 — FinStripe Repository Coverage
Add full unit test coverage for the FinStripe PaymentTransactionRepository layer.
Tests exercise list_for_invoice, update_status, get_by_transfer_id, list_for_vendor,
cross-namespace isolation, and edge cases (offset, limit, unknown IDs).
 
No bugs expected in the repository layer — all tests currently pass.
 
Tests follow the established pattern with:
 

• Title / Basically question / Steps / Expected Results
   
  📁 Test Files
  tests/unit/mcp/test_finstripe_repositories.py
   

TestListForInvoice

Test ID	Title
test_fs_repo_001	list_for_invoice returns matching transactions
test_fs_repo_002	list_for_invoice returns empty when no transactions
test_fs_repo_003	list_for_invoice returns multiple transactions

TestUpdateStatus

Test ID	Title
test_fs_repo_004	update_status changes status and returns transaction
test_fs_repo_005	update_status persists to DB
test_fs_repo_006	update_status returns None for unknown transfer ID

TestGetByTransferId

Test ID	Title
test_fs_repo_007	get_by_transfer_id returns transaction
test_fs_repo_008	get_by_transfer_id returns None when not found

TestListForVendor

Test ID	Title
test_fs_repo_009	list_for_vendor respects limit
test_fs_repo_010	list_for_vendor respects offset
test_fs_repo_011	list_for_vendor scoped to vendor_id
test_fs_repo_012	get_by_transfer_id cross-namespace returns None