fix: let recovery veto scheduled admin operations

[Akinsuyiphilip]

Closes #501

Summary

Align the settlement administrative timelock with the recovery window and make
pending recovery an emergency veto over scheduled administrative operations.

Problem

Scheduled upgrades and admin transfers previously became executable after
48 hours, while recovery required seven days before it could be executed. A
compromised administrator could therefore schedule a malicious upgrade or
admin transfer and have it execute before the recovery address had a chance to
intervene.

This defeated recovery's intended role as a safeguard against compromised
administrative credentials.

Changes

• Increase the minimum settlement scheduled-operation delay from 48 hours to
  seven days.
• Reject execution of scheduled administrative operations while recovery is
  pending.
• Preserve the veto until recovery is either cancelled or executed.
• Document the timelock/recovery timing relationship and threat model.
• Add a regression test covering the recovery/timelock race.

Security behavior

Once recovery is initiated, pending scheduled administrative operations cannot
execute, including upgrades and admin transfers. This remains true even if the
operation's nominal execution time has elapsed. The operation can only proceed
after the pending recovery is cancelled; if recovery executes, administrative
state changes accordingly and the stale scheduled operation remains blocked by
the recovery state transition.

The seven-day timelock also ensures that, absent an already-pending recovery,
the recovery window is not longer than the delay before a scheduled operation
can execute.

Testing

Added:

• recovery_vetoes_scheduled_operation_before_timelock_expiry

Validation performed:

cargo test --workspace

4 common tests passed
59 governance tests passed
88 settlement tests passed
All doc-tests passed

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