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/Models/RoslynQueryRequest.cs

@@ -0,0 +1,65 @@
+using System.ComponentModel.DataAnnotations;
+
+namespace RoslynBridge.WebApi.Models;
+
+/// <summary>
+/// Request model for Roslyn query operations
+/// </summary>
+public class RoslynQueryRequest
+{
+    /// <summary>
+    /// Type of query to execute (e.g., "getsymbol", "getdocument", "findreferences")
+    /// </summary>
+    [Required]
+    public string QueryType { get; set; } = string.Empty;
+
+    /// <summary>
+    /// File path for file-based operations
+    /// </summary>
+    public string? FilePath { get; set; }
+
+    /// <summary>
+    /// Symbol name for symbol-based operations
+    /// </summary>
+    public string? SymbolName { get; set; }
+
+    /// <summary>
+    /// Line number (1-based) for position-based operations
+    /// </summary>
+    public int? Line { get; set; }
+
+    /// <summary>
+    /// Column number (0-based) for position-based operations
+    /// </summary>
+    public int? Column { get; set; }
+
+    /// <summary>
+    /// Additional parameters for the query
+    /// </summary>
+    public Dictionary<string, string>? Parameters { get; set; }
+
+    /// <summary>
+    /// Project name for project operations
+    /// </summary>
+    public string? ProjectName { get; set; }
+
+    /// <summary>
+    /// Package name for NuGet operations
+    /// </summary>
+    public string? PackageName { get; set; }
+
+    /// <summary>
+    /// Version for NuGet package operations
+    /// </summary>
+    public string? Version { get; set; }
+
+    /// <summary>
+    /// Build configuration (Debug/Release)
+    /// </summary>
+    public string? Configuration { get; set; }
+
+    /// <summary>
+    /// Directory path for directory operations
+    /// </summary>
+    public string? DirectoryPath { get; set; }
+}