Feature: send workspace/didDeleteFiles and didChangeWatchedFiles notifications

[nemekath]

Problem

After a file is deleted or renamed in the workspace, the LSP server retains
stale diagnostics for the removed file. workspace_diagnostics continues to
report errors from files that no longer exist.

Root cause

The lsp-mcp-server adapter bridges MCP tool calls to LSP requests but does not
send workspace/didDeleteFiles or workspace/didChangeWatchedFiles
notifications to the language server. The LSP spec defines these notifications
specifically so servers can invalidate their caches.

Current workaround

Call lsp_index_files again after any file creation, deletion, or rename.
This forces a re-scan but is manual and easy to forget.

Suggested fix

Option A (minimal): After lsp_index_files is called, diff the current file
list against the previous one and send workspace/didDeleteFiles for removals.

Option B (complete): Add an fs.watch / chokidar file watcher that sends
workspace/didChangeWatchedFiles notifications automatically when files in
the workspace root change.

Measured impact

Tested with csharp-ls 0.26.0 on a .NET 8 solution (93 test files, 1731 tests).
After deleting a probe file with 3 intentional errors, workspace_diagnostics
continued to report CS0029, CS1061, CS8602 for the deleted file until the
server was restarted.

Environment

• lsp-mcp-server 1.1.20
• csharp-ls 0.26.0
• Windows 11, Node.js 22.21.0

[il-santo]

I don't use windows, but I'll try to fix it anyway.