feat(tools): add symbol_workspace search tool

[CalvinAllen]

Summary

Add a new MCP tool symbol_workspace that searches for symbols across all projects in the solution.

Details

• Iterates through all projects and their items
• Extracts symbols using FileCodeModel
• Filters by query string (case-insensitive contains)
• Returns matching symbols with file locations
• Supports maxResults parameter for performance

Implementation Tasks

• Add SearchWorkspaceSymbolsAsync(string query, int maxResults) to IVisualStudioRpc in RpcContracts.cs
• Add SearchWorkspaceSymbolsAsync to IVisualStudioService.cs
• Implement SearchWorkspaceSymbolsAsync in VisualStudioService.cs
• Add helper method to recursively iterate ProjectItems
• Add forwarding method in RpcServer.cs
• Add proxy method in RpcClient.cs
• Add symbol_workspace tool method to NavigationTools.cs
• Build and verify no errors

Dependencies

• Requires feat(tools): add symbol_document navigation tool #13 (symbol_document) for SymbolModels DTOs

Notes

This is Phase 2 of the LSP-style navigation tools feature. Builds on the symbol extraction pattern from Phase 1.