Add Graph client factory helpers to Teams turn context and app-only overloads

[tracyboehrer]

Summary

Adds Microsoft Graph client factory helpers so agents can obtain a GraphServiceClient for both delegated (user) and app-only (application) tokens without manually wiring up token providers or scopes.

Changes

• New GraphClientFactory — shared by TeamsAgentExtension and TeamsTurnContext, centralizing the token-provider and .default scope-derivation logic (no duplication). Scope/resource is derived from the Graph base URL so national clouds (e.g. graph.microsoft.us) are honored.
• App-only Graph client overloads:
  • GetAppGraphClient(...) — connection resolved from the current turn (ITurnContext.Identity + Activity) via IConnections.GetTokenProvider.
  • GetAppGraphClientForConnection(connectionName, ...) — named token connection. No extra appsettings required beyond the existing token connection.
• Turn-context surface — GetGraphClient / GetAppGraphClient / GetAppGraphClientForConnection are now exposed on ITeamsTurnContext / TeamsTurnContext, resolving UserAuthorization and IConnections from ITurnContext.Services (clear InvalidOperationException if unconfigured).
• AgentApplication.SetTurnContextServices now registers IConnections in turn services so the turn-context helpers can resolve it.

Notes

• The named-connection variant is GetAppGraphClientForConnection (not an overload of GetAppGraphClient) to avoid a silent single-string overload collision with GetAppGraphClient(graphBaseUrl).
• App-only clients use application permissions, so callers specify the target resource in the request path (e.g. client.Users["{userId}"]...).

Testing

• dotnet build src\libraries\Extensions\Microsoft.Agents.Extensions.MSTeams\Microsoft.Agents.Extensions.MSTeams.csproj → 0 warnings / 0 errors.

[Copilot]

Pull request overview

Adds Microsoft Graph GraphServiceClient factory helpers to the MSTeams extension so agents can easily obtain delegated (user) and app-only Graph clients from either TeamsAgentExtension or ITeamsTurnContext, with shared scope/resource derivation via a central factory.

Changes:

• Introduces GraphClientFactory to centralize Graph client creation for delegated and app-only authentication.
• Exposes Graph client helpers on TeamsTurnContext / ITeamsTurnContext and adds app-only overloads (including named-connection).
• Registers IConnections into per-turn services in AgentApplication.SetTurnContextServices so turn-context helpers can resolve it.

Reviewed changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
src/libraries/Extensions/Microsoft.Agents.Extensions.MSTeams/TeamsTurnContext.cs	Adds Graph client helper methods that resolve UserAuthorization / IConnections from turn services.
src/libraries/Extensions/Microsoft.Agents.Extensions.MSTeams/TeamsAgentExtension.cs	Refactors delegated Graph client creation to factory; adds app-only Graph client helpers (turn-resolved + named-connection).
src/libraries/Extensions/Microsoft.Agents.Extensions.MSTeams/ITeamsTurnContext.cs	Adds Graph client helper methods to the public Teams turn-context interface.
src/libraries/Extensions/Microsoft.Agents.Extensions.MSTeams/GraphClientFactory.cs	New shared factory for delegated + app-only Graph client construction and scope derivation.
src/libraries/Builder/Microsoft.Agents.Builder/App/AgentApplication.cs	Registers IConnections into turnContext.Services when configured, enabling turn-context resolution.