Audit trail for project, sandbox, and credential lifecycle actions

Context

Three entities have soft-delete + grace-period purge: credentials, projects, and sandboxes (sandboxes since #4670). Audit coverage is patchy. Today only credentials' hard delete writes an audit row (Audit.user_initiated_event("deleted", ...)). Schedule and cancel on all three entities, plus hard delete on projects and sandboxes, write nothing. Support questions like "who deleted this?" have no clean answer.

Proposal

Add audit rows for the three lifecycle actions (schedule, cancel, hard delete) across all three entities, in one consistent pass. The audit modules already exist (Lightning.Credentials.Audit, Lightning.Projects.Audit); it's mostly inserting the right events in the existing transactions.

Sandboxes are projects, so sandbox audit events live in Lightning.Projects.Audit. Reuse existing event names with a project_type tag, or introduce sandbox-specific event names if that reads cleaner.

Start with the existing hard-delete audit event in Lightning.Credentials.Audit, then inspect the lifecycle transactions for credentials, projects, and sandboxes. Add consistent audit coverage for schedule, cancel, and hard delete, using Lightning.Projects.Audit for sandbox events. Done means all three actions across all three entities produce the intended audit rows, including an agreed project_type or event-name treatment for sandboxes.