#59 FTX-59: Cursor pagination + audit filters + missing routes

Cursor pagination default 25 max 100 (UB-API-7) on inbox/audit/policies/delegations/webhooks; /v1/audit filters decision/actor/time (UB-AUD-3); add GET /v1/tasks/{id}, GET/PATCH /v1/tenants/{id}, GET /v1/reason-codes, POST /v1/decisions/{id}/context. Phase 4.