Fix PostgreSQL DateTime compatibility issue in ActivityController

[Copilot]

Resolves PostgreSQL DateTime compatibility issues when calling GetPendingActivity() that resulted in the error:

Cannot write DateTime with Kind=Local to PostgreSQL type 'timestamp with time zone', only UTC is supported

Problem

PostgreSQL's timestamp with time zone columns require DateTime values with Kind=Utc, but the ActivityController was passing DateTime values with incompatible kinds:

1. _dateTimeProvider.Now (Kind=Local) to GetFirstOpenSubscription
2. DateTime.MaxValue (Kind=Unspecified) for token expiry in SetSubscriptionToken

This caused runtime exceptions when using the PostgreSQL persistence provider with activities.

Solution

Made minimal changes to ActivityController.cs to ensure PostgreSQL compatibility:

// Line 37: Use UTC time for subscription queries
- subscription = await _subscriptionRepository.GetFirstOpenSubscription(Event.EventTypeActivity, activityName, _dateTimeProvider.Now);
+ subscription = await _subscriptionRepository.GetFirstOpenSubscription(Event.EventTypeActivity, activityName, _dateTimeProvider.UtcNow);

// Line 54: Use UTC DateTime.MaxValue for token expiry
- TokenExpiry = DateTime.MaxValue
+ TokenExpiry = new DateTime(DateTime.MaxValue.Ticks, DateTimeKind.Utc)

Impact

• ✅ Fixes PostgreSQL "Cannot write DateTime with Kind=Local" runtime error
• ✅ Preserves exact same date/time values, only corrects DateTimeKind
• ✅ Maintains backward compatibility with all persistence providers (memory, SQL Server, MongoDB, etc.)
• ✅ Aligns with existing patterns used elsewhere in the codebase (e.g., UserStepContainer uses DateTime.Now.ToUniversalTime())

The changes are minimal and surgical, affecting only the specific DateTime handling that caused PostgreSQL compatibility issues while maintaining full functionality across all supported persistence providers.

Fixes #1329.

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