fix(graphql)!: standardize pagination on a single-level shape

[lakhansamani]

Summary

• 6 List*Request input types (ListClients, ListTrustedIssuers, ListSAMLServiceProviders, ListOrganizations, ListOrgDomains, ListOrgMembers) declared their pagination field as PaginatedRequest, a wrapper type whose only field is itself named pagination: PaginationRequest — forcing every caller to double-nest (pagination: { pagination: { limit, page } })
• 3 more operations (_verification_requests, _webhooks, _email_templates) took PaginatedRequest as their entire top-level params type
• This wrapper never existed on the canonical proto/gRPC surface (proto/authorizer/v1/pagination.proto and admin.proto — every List RPC takes PaginationRequest directly, no wrapper), and 4 other GraphQL-only request types (ListUsers, UserOrganizations, ListWebhookLog, ListAuditLog) already embedded PaginationRequest directly
• The double-nesting was a GraphQL-only accident, not intentional API design — and it was actively broken: OrgDomains.tsx (this repo's own dashboard) sent the single-nested shape and got GRAPHQL_VALIDATION_FAILED on every call (see fix(dashboard): send double-nested pagination in OrgDomains' list query #721) until a prior fix matched the wrapper, and authorizer-js's TypeScript types for all 6 List*Request types were already (accidentally) typed as single-nested PaginationRequest, meaning no strictly-typed SDK consumer could construct the double-nested shape the schema required either
• Removes the PaginatedRequest type entirely; the 9 affected fields/params now declare PaginationRequest directly, matching every other GraphQL endpoint and the proto surface
• internal/utils/pagination.go's shared GetPagination helper now takes *model.PaginationRequest directly, eliminating the wrap-then-call boilerplate every "already single-nested" caller needed to reuse it
• The gRPC handler layer's duplicate modelPaginatedRequest/modelPaginationRequest converters collapse into one
• Every consumer in this repo (internal/service, internal/graphql, internal/grpcsrv/handlers, web/dashboard) is updated to match

Note: this branch includes OrgDomains.tsx's pagination-nesting fix and error handling inline (originally #721, still open) since both PRs touch the same lines — whichever merges first, the other will show as a no-op on that overlap.

Coordinated SDK fixes (each needs releasing alongside this): authorizer-js#50, authorizer-go#22, authorizer-py#7.

Test plan

• go build ./... / go vet ./... / make lint-go clean
• Full go test ./internal/... (SQLite) clean, no regressions
• New TestGetPagination unit test covering nil/empty/explicit-values cases
• web/dashboard: npm run build clean, full 43-test vitest suite passes (including the updated OrgDomains.test.tsx regression test asserting the correct single-nested shape)
• Reviewed by an independent pass (opus-tier) verifying the proto-layer claim, a repo-wide grep for zero remaining PaginatedRequest references, every Go call site's value-flow, and both distinct dashboard fix shapes (5 endpoints unwrap one level; Webhooks/EmailTemplates drop the wrapper key entirely) — approved, zero findings