[Agent Archiving] Payables and Expense agent implementation for IAgentArchiving - #10460

What & why

Honours the new IAgentArchiving interface, and opts Payables Agent and Expense Agent out of archiving.

The Archive action is disabled on the Agent List and Agent Card for agent types that do not support archiving, and Agent.Archive blocks it programmatically so the guard cannot be bypassed. The check runs off the record the pages already hold, so it costs no extra read and cannot fail on an unsaved record.

Payables and Expense opt out via their own PA Agent Archiving / EA Agent Archiving codeunits, mirroring how each app already registers IAgentTaskExecution, so they can be removed cleanly once each agent supports archiving. Both are single-instance: the setup record enforcing that is left behind by archiving, which would block creating a replacement.

Behaviour is unchanged for every agent type that does not opt out.

Linked work

AB#647379

Related PRs

Cross-repo change - merge in this order:

1. BC-Platform - the interface: https://microsoft.ghe.com/bic/BC-Platform/pull/46005
2. BCApps - System App honours it, Payables and Expense opt out (this PR): [Agent Archiving] Payables and Expense agent implementation for IAgentArchiving #10460

Note: this PR will not build until 1 is merged and a platform version carrying IAgentArchiving flows through.