fix(persistence): add AuditableEntitySaveChangesInterceptor with async-safe recursion guard

[iammukeshm]

Summary

Supersedes #1223 — rebased onto latest develop with critical bug fixes applied.

• AuditableEntitySaveChangesInterceptor: Automatically populates IAuditableEntity audit metadata and converts ISoftDeletable deletes into soft-delete updates
• Async-safe recursion guard: Uses AsyncLocal<bool> (not [ThreadStatic]) to prevent StackOverflowException from nested SaveChanges calls
• Global registration: Interceptor registered via AddHeroDatabaseOptions alongside DomainEventsInterceptor

Changes from original PR (#1223)

Fix	Detail
[ThreadStatic] → AsyncLocal<bool>	Original guard was broken for async code — after await, execution can resume on a different thread
Extensions → EntityEntryExtensions	Renamed to internal static class to avoid namespace pollution
Added .ConfigureAwait(false)	On all await calls per project conventions
Added ArgumentNullException.ThrowIfNull	Guard clauses on eventData to fix CA1062 warnings
TryAddSingleton for TimeProvider	Prevents duplicate registration
Merge conflict resolved	PersistenceExtensions.cs merged cleanly with existing DomainEventsInterceptor registration

Test plan

• dotnet build src/FSH.Framework.slnx — 0 errors, 0 new warnings
• Verify audit fields are populated on entity create/update
• Verify soft-delete converts DELETE → UPDATE with metadata
• Verify no StackOverflow on nested SaveChanges scenarios

Credit: @cesarcastrocuba (original implementation in #1223)

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