fix(api): default EmployeeInvite.Status to Pending so accept-by-code works

[bllr777]

Why

Newly created employee invites were saved with Status = 0 because:

• EmployeeInviteStatus.Pending is 1, not 0.
• EmployeeInvite.Status had no default initializer, so it defaulted to (EmployeeInviteStatus)0.
• InviteAsync never assigned Status explicitly before insert.

Result: GET /api/employeeinvite/{code} filters by Status == Pending (1) and always returned 404 for freshly created invites - exactly what staging saw with code N72cZl.

What changed

• EmployeeInvite.Status now initialized to EmployeeInviteStatus.Pending.
• InviteAsync also sets invite.Status = EmployeeInviteStatus.Pending explicitly (belt + suspenders, in case the caller passes a partially populated entity).
• Fixed pre-existing bug in the duplicate-invite check: it was filtering by invite.Status (the new invite, always Pending after this fix) instead of e.Status (the row being scanned). Now correctly checks for an existing Pending invite for the same email.

Verification

• dotnet build - 0 errors, 0 warnings.
• dotnet test - 54/54 passing.
• Staging row N72cZl hot-patched to Status = 1; full GET-by-code path verified to behave correctly with the new defaults.