refactor(nib): require supporting documents for NIB changes Closes #1741. ## Changes The existing NIB pages only allow uploading a missing document. Dashboard staff and linked taxpayers can now change the NIB number by supplying a new supporting PDF and a reason. - Validate the NIB format, PDF MIME type and file header, nonempty content, and 10MB upload limit. Reject duplicate numbers, stale submissions, and changes without current account ownership. - Save the number, document, and audit entry together. Preserve previous documents, remove failed uploads, and clear company verification after an identity change. - Protect the existing dashboard uploader against concurrent NIB changes, refresh sensitive viewers after saving, and route the taxpayer profile's NIB button to the NIB page. ## Release impact Patch. This extends the existing taxpayer identity and NIB document workflow, so the title uses `refactor`. ## Migration notes No database migration, new dependency, or configuration change is required. Each number change requires a fresh PDF, and the company must be verified again afterward. Matching the entered number to the document contents remains part of human verification. ## Validation - Passed the UI integration, primary foreground, table-card, and page-header policy checks against base `d36390d8bc72d4c9b054bb67115b58eb9b676e37`. - Passed ESLint and targeted TypeScript analysis of all 10 changed files with no diagnostics. - Passed React Doctor changed-source audit against the same base with zero errors, zero warnings, and no skipped checks. - Added regression coverage for required PDFs, stale data, revoked access, duplicate or unchanged numbers, audit rollback, and retaining documents after cache refresh failures. Tests remain unrun as instructed. - Build, test, and development server commands were not run. <!-- This is an auto-generated comment: release notes by coderabbit.ai --> <!-- coderabbit-ai-generated:v1 --> ## Summary by CodeRabbit * **New Features** * Business taxpayers can request a change to their NIB from the taxpayer dashboard or self-service area by submitting a replacement number, PDF document, and reason. * After a change, the NIB requires reverification. * **Bug Fixes** * Improved safeguards for NIB updates: requests are rejected when taxpayer details have changed or the replacement number is already in use. * Failed document uploads are cleaned up, and cache refresh issues no longer undo a completed change. <!-- end of auto-generated comment: release notes by coderabbit.ai -->