Let an admin grant a specific cron narrow admin-read access for unattended fires (#471)

Unattended cron fires cannot use the admin API — autonomous turns are refused admin capability, which is the right default but blocks legitimately unattended workflows such as a cron that reads conversation transcripts to find and file fixes for user-visible failures. Rather than weakening that gate, an org admin can now — only on an attended turn they started themselves — imbue one specific cron with a narrow, explicit admin-read grant. Fire-time turns receive exactly that grant and nothing more: grants are forwarded through the turn pipeline, stripped at the external boundary, re-checked when the cron runs, and dropped to the floor on any raw tampering. Any capability beyond the grant still requires a human.

**Deployment notes**

Crons gain an optional persisted unattendedGrants field via the DurableMap JSON store — old
rows read fine, and rollback is safe (old code simply ignores the field, and run/enable re-checks
mean a stale grant can't fire without the checks on new code)
Capability tokens gain an optional grants claim; verification only type-checks it when present, and
old instances in the blue-green window ignore unknown claims rather than rejecting the token
Feature is opt-in and tightly gated: personal-scope, runs-as-owner crons whose owner is a live
org admin; grants are stripped at the external boundary and re-validated at fire time — no default
behavior change for orgs
OriginalforkPR:Cronunattendedadmin-readgrants(continuous-improvementloopMVP)

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