feat: structured approval grants (beyond boolean approve/deny)

[arthurpanhku]

Why (roadmap: Next)

Approvals today are per-call booleans (requestApproval(id, toolName, input)). Regulated teams need scoped grants: who approved what, for which scope, until when — recorded as evidence.

Sketch

• Grant shape: { subject, toolName, scope (e.g. command pattern/path glob), expiresAt | forRun }.
• 'Allow npm test for the rest of this run' instead of clicking approve N times.
• Grants checked at the registry.run chokepoint after policy; every grant + use recorded in the audit chain.
• UX: the approval prompt offers 'once / for this run / always for this session'.

Constraints

Policy still wins (a grant can never widen org policy); grants are narrowing-only sugar on top. Design doc first.

[arthurpanhku]

🌱 Frontend-only good-first-issue carved out for newcomers: #136 ('Allow for this run' option, UI only). Backend grant semantics stay here.