Add WebAPI middleware for multi-instance Roslyn Bridge routing

Add RoslynBridge.WebApi - ASP.NET Core 8.0 middleware that:
- Provides a centralized REST API for accessing multiple VS instances
- Manages instance registry with discovery by port, solution, or PID
- Proxies requests to the appropriate VS instance
- Tracks request/response history for debugging
- Auto-cleanup of stale instances via background service

Features:
- Health endpoints: /api/health, /api/health/ping
- Roslyn endpoints: /api/roslyn/projects, /api/roslyn/diagnostics, etc.
- Instance management: /api/instances (register, heartbeat, unregister)
- History tracking: /api/history, /api/history/stats
- Swagger UI at root (/) for API documentation
- CORS enabled for web applications

Services:
- InstanceRegistryService: Thread-safe registry of VS instances
- HistoryService: In-memory request/response history (max 1000 entries)
- InstanceCleanupService: Background service to remove stale instances
- RoslynBridgeClient: HTTP client for proxying to VS instances

Update RoslynBridge.sln to include RoslynBridge.WebApi project.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

RoslynBridge.WebApi/Services/RoslynBridgeClient.cs

@@ -0,0 +1,174 @@
+using System.Text;
+using System.Text.Json;
+using RoslynBridge.WebApi.Models;
+
+namespace RoslynBridge.WebApi.Services;
+
+/// <summary>
+/// HTTP client for communicating with the Roslyn Bridge Visual Studio plugin
+/// </summary>
+public class RoslynBridgeClient : IRoslynBridgeClient
+{
+    private readonly HttpClient _httpClient;
+    private readonly IInstanceRegistryService _registryService;
+    private readonly ILogger<RoslynBridgeClient> _logger;
+    private readonly JsonSerializerOptions _jsonOptions;
+
+    public RoslynBridgeClient(
+        HttpClient httpClient,
+        IInstanceRegistryService registryService,
+        ILogger<RoslynBridgeClient> logger)
+    {
+        _httpClient = httpClient;
+        _registryService = registryService;
+        _logger = logger;
+        _jsonOptions = new JsonSerializerOptions
+        {
+            PropertyNameCaseInsensitive = true,
+            PropertyNamingPolicy = JsonNamingPolicy.CamelCase
+        };
+    }
+
+    public async Task<RoslynQueryResponse> ExecuteQueryAsync(
+        RoslynQueryRequest request,
+        int? instancePort = null,
+        CancellationToken cancellationToken = default)
+    {
+        try
+        {
+            var targetPort = await ResolveInstancePortAsync(instancePort, request);
+
+            if (targetPort == null)
+            {
+                return new RoslynQueryResponse
+                {
+                    Success = false,
+                    Error = "No Visual Studio instance available"
+                };
+            }
+
+            _logger.LogInformation("Executing query: {QueryType} on port {Port}", request.QueryType, targetPort);
+
+            var json = JsonSerializer.Serialize(request, _jsonOptions);
+            var content = new StringContent(json, Encoding.UTF8, "application/json");
+
+            var url = $"http://localhost:{targetPort}/query";
+            var response = await _httpClient.PostAsync(url, content, cancellationToken);
+
+            if (!response.IsSuccessStatusCode)
+            {
+                var errorContent = await response.Content.ReadAsStringAsync(cancellationToken);
+                _logger.LogError("Query failed with status {StatusCode}: {Error}", response.StatusCode, errorContent);
+
+                return new RoslynQueryResponse
+                {
+                    Success = false,
+                    Error = $"Request failed with status {response.StatusCode}: {errorContent}"
+                };
+            }
+
+            var responseContent = await response.Content.ReadAsStringAsync(cancellationToken);
+            var result = JsonSerializer.Deserialize<RoslynQueryResponse>(responseContent, _jsonOptions);
+
+            if (result == null)
+            {
+                return new RoslynQueryResponse
+                {
+                    Success = false,
+                    Error = "Failed to deserialize response"
+                };
+            }
+
+            _logger.LogInformation("Query executed successfully: {Success}", result.Success);
+            return result;
+        }
+        catch (HttpRequestException ex)
+        {
+            _logger.LogError(ex, "HTTP request failed while executing query");
+            return new RoslynQueryResponse
+            {
+                Success = false,
+                Error = $"Failed to connect to Roslyn Bridge server: {ex.Message}"
+            };
+        }
+        catch (Exception ex)
+        {
+            _logger.LogError(ex, "Unexpected error while executing query");
+            return new RoslynQueryResponse
+            {
+                Success = false,
+                Error = $"Unexpected error: {ex.Message}"
+            };
+        }
+    }
+
+    public async Task<bool> IsHealthyAsync(int? instancePort = null, CancellationToken cancellationToken = default)
+    {
+        try
+        {
+            var targetPort = await ResolveInstancePortAsync(instancePort, null);
+
+            if (targetPort == null)
+            {
+                return false;
+            }
+
+            var request = new RoslynQueryRequest { QueryType = "health" };
+            var json = JsonSerializer.Serialize(request, _jsonOptions);
+            var content = new StringContent(json, Encoding.UTF8, "application/json");
+
+            var url = $"http://localhost:{targetPort}/health";
+            var response = await _httpClient.PostAsync(url, content, cancellationToken);
+            return response.IsSuccessStatusCode;
+        }
+        catch (Exception ex)
+        {
+            _logger.LogWarning(ex, "Health check failed");
+            return false;
+        }
+    }
+
+    /// <summary>
+    /// Resolves which VS instance port to use based on provided hints
+    /// </summary>
+    private Task<int?> ResolveInstancePortAsync(int? explicitPort, RoslynQueryRequest? request)
+    {
+        // If explicit port specified, use it
+        if (explicitPort.HasValue)
+        {
+            return Task.FromResult<int?>(explicitPort.Value);
+        }
+
+        // Try to find instance by solution path from request
+        if (request != null && !string.IsNullOrEmpty(request.FilePath))
+        {
+            // Extract solution path by looking for .sln file in the path hierarchy
+            var directory = Path.GetDirectoryName(request.FilePath);
+            while (!string.IsNullOrEmpty(directory))
+            {
+                var solutionFiles = Directory.GetFiles(directory, "*.sln");
+                if (solutionFiles.Length > 0)
+                {
+                    var instance = _registryService.GetBySolutionPath(solutionFiles[0]);
+                    if (instance != null)
+                    {
+                        _logger.LogDebug("Found instance by solution path: {SolutionPath}", solutionFiles[0]);
+                        return Task.FromResult<int?>(instance.Port);
+                    }
+                }
+                directory = Path.GetDirectoryName(directory);
+            }
+        }
+
+        // Fall back to first available instance
+        var instances = _registryService.GetAllInstances().ToList();
+        if (instances.Any())
+        {
+            _logger.LogDebug("Using first available instance: port {Port}", instances[0].Port);
+            return Task.FromResult<int?>(instances[0].Port);
+        }
+
+        _logger.LogWarning("No Visual Studio instances registered");
+        return Task.FromResult<int?>(null);
+    }
+}