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/IHistoryService.cs

@@ -0,0 +1,46 @@
+using RoslynBridge.WebApi.Models;
+
+namespace RoslynBridge.WebApi.Services;
+
+/// <summary>
+/// Service for managing query history
+/// </summary>
+public interface IHistoryService
+{
+    /// <summary>
+    /// Add a new history entry
+    /// </summary>
+    /// <param name="entry">The history entry to add</param>
+    void Add(QueryHistoryEntry entry);
+
+    /// <summary>
+    /// Get all history entries
+    /// </summary>
+    /// <returns>List of all history entries</returns>
+    IEnumerable<QueryHistoryEntry> GetAll();
+
+    /// <summary>
+    /// Get a specific history entry by ID
+    /// </summary>
+    /// <param name="id">The entry ID</param>
+    /// <returns>The history entry, or null if not found</returns>
+    QueryHistoryEntry? GetById(string id);
+
+    /// <summary>
+    /// Get recent history entries
+    /// </summary>
+    /// <param name="count">Number of entries to return</param>
+    /// <returns>List of recent history entries</returns>
+    IEnumerable<QueryHistoryEntry> GetRecent(int count = 50);
+
+    /// <summary>
+    /// Clear all history entries
+    /// </summary>
+    void Clear();
+
+    /// <summary>
+    /// Get total count of history entries
+    /// </summary>
+    /// <returns>Total number of entries</returns>
+    int GetCount();
+}