Improve API surface and property accessibility

[ChuckNovice]

Summary

• Make Domain classes internal to hide implementation details from library consumers
• Make repository interfaces and MongoDB providers internal
• Change CreateRecurrenceAsync and CreateOccurrenceAsync to return CalendarEntry instead of domain types
• Update CalendarEntry property accessibility with proper immutability rules
• Allow Type and ResourcePath changes on standalone occurrences (previously blocked)
• Add OriginalResourcePath tracking for database lookups when ResourcePath is modified

Breaking Changes

Change	Before	After
CreateRecurrenceAsync return type	Task<Recurrence>	Task<CalendarEntry>
CreateOccurrenceAsync return type	Task<Occurrence>	Task<CalendarEntry>
Domain classes visibility	public	internal
Repository interfaces visibility	public	internal
CalendarEntry.Organization	set	init (immutable)
CalendarEntry.EntryType	set	init (immutable)
CalendarEntry.TimeZone	set	init (immutable)
CalendarEntry.EndTime	set	internal set
CalendarEntry IDs	set	init (immutable)
Standalone occurrence Type/ResourcePath	immutable	mutable

Property Mutability Rules

Always mutable: StartTime, Duration, Extensions

Mutable on standalone occurrences and recurrences only: Type, ResourcePath

Always immutable: Organization, EntryType, TimeZone, RecurrenceId, OccurrenceId, OverrideId, ExceptionId, RecurrenceDetails, Original

Test plan

• Build succeeds
• All 131 unit tests pass
• Type change on standalone occurrence now succeeds (previously failed)
• Type/ResourcePath changes on virtualized occurrences still blocked

🤖 Generated with Claude Code