Do not infer organization-wide access from missing team memberships

Observation (2026-09-03 UTC, source: read-only review of the uncommitted COR-3971 Shield dashboard diff and docs/org-access-policies.md): assignment-picker grouping must keep team membership separate from load visibility scope. A candidate with no team memberships can still have only own visibility (for example, a teamless load creator), while an org-wide Admin can belong to teams. Labeling the former “Organization-wide” or the latter only by team produces a false authorization cue even when the server-side eligibility and write checks remain correct. Carry explicit scope/group semantics from the eligibility owner instead of inferring them from an empty teams array.