.NET: Bump Azure.AI.Projects to 2.1.0-beta.2 and add agent-endpoint AsAIAgent path (#5899)

* .NET: Bump Azure.AI.Projects to 2.1.0-beta.2 and add agent-endpoint AsAIAgent path

Bumps Azure.AI.Projects to 2.1.0-beta.2 with the matching transitive pins (Azure.Core 1.55.0, System.ClientModel 1.11.0).

Foundry agent endpoint plumbing:
* FoundryAgent now routes the agent-endpoint constructor through the new GetProjectResponsesClientForAgentEndpoint helper.
* Adds an internal FoundryAgent ctor that takes an existing AIProjectClient plus a parsed agent endpoint so the public extension does not need to construct a second project client.
* Adds public AIProjectClient.AsAIAgent(Uri agentEndpoint, ...) extension. This is the path consumer samples are expected to use for hosted agents because version selection happens server-side.
* Trims the dangling "If you want to construct a FoundryAgent against a project endpoint..." sentence from ParseAgentEndpoint.

Unit tests:
* Four new tests in AzureAIProjectChatClientExtensionsTests cover the AIProjectClient.AsAIAgent(Uri agentEndpoint, ...) overload. 263/263 pass.

Consumer samples (Using-Samples):
* SimpleAgent and SessionFilesClient now read AZURE_AI_PROJECT_ENDPOINT and AZURE_AI_AGENT_NAME (both required, throw on missing), derive the agent endpoint with new Uri($"{projectEndpoint}/agents/{agentName}/endpoint/protocols/openai"), then call aiProjectClient.AsAIAgent(agentEndpoint, ...).
* SessionFilesClient README updated.

Contributor samples (responses/*):
* New HostedContributorRouteExtensions.MapDevTemporaryLocalAgentEndpoint() wildcard route extension so localhost contributor servers accept the per-agent OpenAI endpoint shape the production Hosted runtime exposes.
* All 11 contributor Program.cs files call MapDevTemporaryLocalAgentEndpoint() with a contributor-only warning comment.
* Hosted-Files and Hosted-AzureSearchRag were importing Hosted_Shared_Contributor_Setup but never calling AddDevTemporaryLocalContributorSetup(). Both now call it so HostedSessionIsolationKeyProvider resolves correctly in dev.
* Hosted-AzureSearchRag, Hosted-Files, Hosted-MemoryAgent csprojs drop stale VersionOverride="2.1.0-beta.1" pins.
* Hosted-AzureSearchRag and Hosted-Files csprojs add ProjectReference to Hosted_Shared_Contributor_Setup.
* Hosted-Observability/.dockerignore removed the out/ exclusion that was blocking COPY out/ . in Dockerfile.contributor.

Verified:
* Full solution-scoped build of changed projects: green.
* Scoped CI-parity dotnet format via WSL2 + Docker (mcr.microsoft.com/dotnet/sdk:10.0) over every changed csproj: clean.
* Foundry unit tests: 263/263.
* Contributor docker smoke for 8 hosted samples (publish + docker build + docker run + curl POST to the wildcard route): HTTP 200 / 500 with route matched.
* End-to-end smoke against the real Azure Foundry project with a fresh bearer token: Hosted-Files contributor container served HTTP 200, the agent invoked ListBundledFiles, and returned the expected file name.

* Address PR review: forward pipeline settings; add UTs

- CreateProjectClientOptions also carries RetryPolicy, NetworkTimeout, ClientLoggingOptions, MessageLoggingPolicy (was Transport+UserAgentApplicationId only).

- Make CreateProjectClientOptions internal so tests can verify the copy directly.

- Add AsAIAgent(Uri) UTs covering tools forwarding to inner ChatOptions and null tools handling.

- Add CreateProjectClientOptions UTs covering null caller and full pipeline-settings copy.

dotnet/samples/04-hosting/FoundryHostedAgents/responses/Using-Samples/SessionFilesClient/Program.cs

@@ -1,7 +1,6 @@
 // Copyright (c) Microsoft. All rights reserved.
 
 using System.ClientModel.Primitives;
-using Azure.AI.Extensions.OpenAI;
 using Azure.AI.Projects;
 using Azure.Identity;
 using DotNetEnv;
@@ -11,28 +10,34 @@ using Microsoft.Agents.AI.Foundry;
 // Load .env file if present (for local development)
 Env.TraversePath().Load();
 
-Uri agentEndpoint = new(Environment.GetEnvironmentVariable("AGENT_ENDPOINT")
-    ?? "http://localhost:8088");
+// AZURE_AI_PROJECT_ENDPOINT is the Foundry project endpoint. Shape:
+//   https://<host>/api/projects/<project>
+Uri projectEndpoint = new(Environment.GetEnvironmentVariable("AZURE_AI_PROJECT_ENDPOINT")
+    ?? throw new InvalidOperationException("AZURE_AI_PROJECT_ENDPOINT is not set."));
 
-var agentName = Environment.GetEnvironmentVariable("AGENT_NAME")
-    ?? throw new InvalidOperationException("AGENT_NAME is not set.");
+// AZURE_AI_AGENT_NAME is the registered server-side agent name.
+string agentName = Environment.GetEnvironmentVariable("AZURE_AI_AGENT_NAME")
+    ?? throw new InvalidOperationException("AZURE_AI_AGENT_NAME is not set.");
 
-// ── Create an agent-framework agent backed by the remote Hosted-Files agent ──
+// Derive the per-agent OpenAI endpoint that hosted Foundry agents require.
+Uri agentEndpoint = new($"{projectEndpoint}/agents/{agentName}/endpoint/protocols/openai");
+
+// ── Create an agent-framework agent backed by the remote agent endpoint ──────
 
 var options = new AIProjectClientOptions();
 
-if (agentEndpoint.Scheme == "http")
+if (projectEndpoint.Scheme == "http")
 {
     // For local HTTP dev: tell AIProjectClient the endpoint is HTTPS (to satisfy
     // BearerTokenPolicy's TLS check), then swap the scheme back to HTTP right
     // before the request hits the wire.
-
+    projectEndpoint = new UriBuilder(projectEndpoint) { Scheme = "https" }.Uri;
     agentEndpoint = new UriBuilder(agentEndpoint) { Scheme = "https" }.Uri;
     options.AddPolicy(new HttpSchemeRewritePolicy(), PipelinePosition.BeforeTransport);
 }
 
-var aiProjectClient = new AIProjectClient(agentEndpoint, new AzureCliCredential(), options);
-FoundryAgent agent = aiProjectClient.AsAIAgent(new AgentReference(agentName));
+var aiProjectClient = new AIProjectClient(projectEndpoint, new AzureCliCredential(), options);
+FoundryAgent agent = aiProjectClient.AsAIAgent(agentEndpoint);
 
 AgentSession session = await agent.CreateSessionAsync();
 
@@ -41,10 +46,10 @@ AgentSession session = await agent.CreateSessionAsync();
 Console.ForegroundColor = ConsoleColor.Cyan;
 Console.WriteLine($"""
     ══════════════════════════════════════════════════════════
-    Session Files Client                                    
+    Session Files Client
     Connected to: {agentEndpoint}
     Try: "Give me the total revenue in the contoso file."
-    Type a message or 'quit' to exit                        
+    Type a message or 'quit' to exit
     ══════════════════════════════════════════════════════════
     """);
 Console.ResetColor();