Staff tools: moderation, ticket triage, verification review on mobile (staffTools flag)

[teetangh]

Context

staff/ routes are gated by featureGate middleware (FeatureFlags.staffTools = false); staff/admin users currently land on the standard 5-tab layout instead of the staff tab set (lib/app/providers/navigation_provider.dart switches on the flag).

Scope

1. Staff dashboard screens are UI stubs — build ticket queue, feedback review, verification review, moderation queue against the existing staff/ routes
2. Audit staff routes against the synced schema (ModerationReport.assignedToId, Dispute.assignedToUserId, new SupportTicket links)
3. Decide whether mobile staff tooling is even wanted for MVP+1, or whether staff stays web-only (in which case delete the stubs and the staff tab set)
4. Flip FeatureFlags.staffTools (or remove it)