Extension point: custom delete behavior

[hpehl]

Parent: #320

Summary

Allow resources to customize the delete confirmation dialog and pre/post-delete actions. Currently, DeleteResourceDialog shows a simple confirmation with no way to warn about dependencies, show impact, or perform cleanup.

Motivation

• Pre-delete validation — warn about dependent resources or active connections before confirming (e.g., "This datasource is referenced by 3 persistence units")
• Custom confirmation content — show what will be affected (e.g., "This credential store contains 5 aliases that will also be removed")
• Post-delete actions — cleanup operations after deletion (e.g., removing orphaned child resources, refreshing related views)
• Delete prevention — some resources shouldn't be deletable via the generic UI (e.g., the default datasource, the management security realm)

Capabilities

• Pre-delete check — a function that returns a warning message or blocks deletion entirely
• Custom confirmation dialog — replace the default confirmation with resource-specific content
• Post-delete handler — execute additional operations after successful deletion
• Delete guard — prevent deletion for specific resources based on runtime state

Registration

A registry keyed by Environment + AddressTemplate. When DialogBricks.deleteResourceModal() is called for a matching template, the registry provides the customizations.

Affected Call Sites

• ModelBrowser.delete() — model browser delete action
• FinderBricks — finder column delete action
• ResourceList — resource list remove button

Open Questions

• Should pre-delete checks be async (e.g., query the server for dependent resources)?
• How should the delete guard interact with RBAC — should it be a separate concern or combined?