rest: conditional create/update/delete emit no subscription events; no-match conditional delete audits no entity

[aacruzgon]

Summary

The conditional HTTP handlers write resources without emitting subscription events, so rest-hook (and every other channel) subscribers miss creates, updates and deletes performed via If-None-Exist, PUT [type]?[criteria], or DELETE [type]?[criteria]. Discussion #59 defines the event evaluator as running "on each resource write (create/update/delete)".

Evidence

• crates/rest/src/handlers/create.rs:232-243 emits emit_subscription_event(..., ResourceEventType::Create) on the unconditional path only. The If-None-Exist branch (:117-205) returns before reaching it, so a resource created by conditional create is never announced.
• update.rs: update_handler emits at :285-300 (Create or Update depending on created). conditional_update_handler (:333-464) contains no subscription_engine reference; both the Updated arm and the created-by-upsert arm are silent.
• delete.rs: the instance path emits emit_delete_event at :201-212; conditional_delete_handler (:239-307) emits nothing.
• patch.rs: patch_handler emits at :146-156; conditional_patch_handler does not. (That handler currently has no route; see the PATCH issue.)

Related audit gap in the same handler: conditional_delete_handler's NoMatch arm (delete.rs:298-301) answers 204 without an AuditResponseContext, so a no-match conditional delete is audited with no entity. The Deleted arm was fixed in #860.

Proposed fix

Emit through the same helpers the unconditional handlers use, in each conditional success arm (Created, Exists is not a write, Updated, Deleted). Add an AuditResponseContext naming the resource type on NoMatch. Tests: a rest-hook subscription receiving a notification for each conditional interaction (the subscriptions crate's channel tests are the model).

Found while validating #511 (see PR #860).