rysweet-4677-rename-agents-project-to-core-trim-dependencies

[rysweet]

• renames Agents to Core
• New project Agents just includes base agents
• Core should just depend on Contracts

Why are these changes needed?

• improves dependencies and makes tests/refactor easier

Related issue number

closes #4677

Checks

• I've included any doc changes needed for https://microsoft.github.io/autogen/. See https://microsoft.github.io/autogen/docs/Contribute#documentation to build and test documentation locally.
• I've added tests (if relevant) corresponding to the changes introduced in this PR.
• I've made sure all auto checks have passed.

Copilot reviewed 36 out of 51 changed files in this pull request and generated no comments.

Files not reviewed (15)

• dotnet/AutoGen.sln: Language not supported
• dotnet/samples/Hello/HelloAIAgents/HelloAIAgents.csproj: Language not supported
• dotnet/samples/Hello/HelloAgent/HelloAgent.csproj: Language not supported
• dotnet/samples/Hello/HelloAgentState/HelloAgentState.csproj: Language not supported
• dotnet/samples/dev-team/DevTeam.AgentHost/DevTeam.AgentHost.csproj: Language not supported
• dotnet/samples/dev-team/DevTeam.Agents/DevTeam.Agents.csproj: Language not supported
• dotnet/samples/dev-team/DevTeam.Backend/DevTeam.Backend.csproj: Language not supported
• dotnet/samples/dev-team/DevTeam.Agents/DeveloperLead/DeveloperLead.cs: Evaluated as low risk
• dotnet/samples/Hello/HelloAgentState/Program.cs: Evaluated as low risk
• dotnet/samples/dev-team/DevTeam.Agents/ProductManager/ProductManager.cs: Evaluated as low risk
• dotnet/samples/dev-team/DevTeam.Agents/Developer/Developer.cs: Evaluated as low risk
• dotnet/samples/dev-team/DevTeam.Backend/Agents/Hubber.cs: Evaluated as low risk
• dotnet/samples/dev-team/DevTeam.Backend/Program.cs: Evaluated as low risk
• dotnet/samples/dev-team/DevTeam.Backend/Agents/AzureGenie.cs: Evaluated as low risk
• dotnet/samples/dev-team/DevTeam.Backend/Services/GithubWebHookProcessor.cs: Evaluated as low risk