Route outbound and subscription-validation to in-process handlers once DIS IP is whitelisted

[martivj]

Description

Once the platform has migrated to DIS and subscribers have whitelisted the main Events API's new outbound IP, route outbound event delivery and subscription validation to in-process Wolverine handlers instead of the Azure Functions built in #1073. Registration and inbound already run fully in-process — this is the last piece, and once it's done Events.Functions has nothing left running in it.

What needs to be done

1. Confirm subscribers have whitelisted the main Events API's new (post-DIS) IP.
2. Turn on the listener flags for SendEventToSubscriberHandler and ValidateSubscriptionHandler (in place but dormant since the restructuring work in Restructure Wolverine handlers into Publisher/Handler/Policy pattern with per-queue feature flags #1072).
3. Route outbound/validation traffic to those handlers instead of EventsAsbOutbound and the ASB-triggered validation function. Open question to resolve as part of this issue: whether that's a straightforward listener swap on the same ASB queue (only one consumer can win each message, so the swap needs to happen cleanly), or whether it needs a second queue name so both the Function and the in-process handler can run side by side for a drain window first — same pattern used for the original Storage Queue → ASB cutover, just one layer deeper.
4. Confirm the Functions have drained any in-flight messages.
5. Delete the Events.Functions project entirely — nothing is left running in it.

Removing the now-dead feature flags, and any other remaining cleanup, will be their own follow-up issues once this lands.