Rename AddProfileSource to AddCompletionClient

[MikeAlhayek]

This pull request refactors the AI client/provider registration system in the CrestApps.Core.AI library, replacing the legacy "profile" terminology and APIs with a new, clearer "completion client" model. The changes affect both the implementation and documentation, improving consistency and paving the way for future extensibility.

Key changes include:

API and Data Model Refactoring:

• Replaces the obsolete AIProfileProviderEntry and "profile source" registration with a new AICompletionClientEntry and "completion client" registration system, updating all relevant code, extension methods, and documentation to use the new terminology and data structures. (AIProfileProviderEntry.cs removed, AICompletionClientEntry.cs added, AIOptions.cs, ServiceCollectionExtensions.cs, architecture.md, ai-core.md) [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13] [14]

• Updates all AI provider registration helpers (Ollama, OpenAI, Azure OpenAI, Azure AI Inference) to use the new AddCoreAICompletionClient<TClient> method instead of the old AddCoreAIProfile<TClient>. (ServiceCollectionExtensions.cs in each provider package) [1] [2] [3] [4]

Documentation and Naming Consistency:

• Updates documentation and release notes to reflect the new "completion client" terminology, replacing all references to "profile" and "profile source" with "completion client" and "completion client entry". (changelog/v1.0.0.md, ai-core.md, architecture.md) [1] [2] [3] [4] [5] [6]

Testing:

• Updates and extends tests to verify that completion clients are correctly registered and available through AIOptions.CompletionClients. (AIProviderConnectionOptionsTests.cs) [1] [2]

These changes modernize the AI provider registration approach, improve clarity for users and maintainers, and ensure a consistent, future-proof API surface.