feat(tooling): add Language Server Protocol (LSP) implementation

[eddmann]

Summary

Implement a Language Server Protocol (LSP) server for santa-lang to enable IDE integration and editor support.

Description

Create an LSP server that provides rich language features for santa-lang in any LSP-compatible editor (VS Code, Neovim, Emacs, Helix, etc.).

Proposed Features

Core LSP Features

• Syntax error diagnostics (real-time error highlighting)
• Go to definition
• Find references
• Hover information (function signatures, types, documentation)
• Auto-completion (keywords, builtins, user-defined symbols)
• Document symbols (outline view)
• Workspace symbols (project-wide search)

Advanced Features

• Rename symbol (across files)
• Code formatting (integrate with formatter when available)
• Signature help (parameter hints)
• Inlay hints (type annotations, parameter names)
• Semantic highlighting
• Code actions (quick fixes, refactorings)

Editor Extensions

• VS Code extension packaging
• Neovim configuration guide
• Other editor setup documentation

CLI Interface

# Start the LSP server
santa lsp

# Start with specific transport
santa lsp --stdio
santa lsp --tcp --port 9257

Implementation Considerations

• Build on existing parser/AST infrastructure
• Use tower-lsp (Rust) or vscode-languageserver (TypeScript) depending on implementation
• Incremental parsing for performance on large files
• Consider caching for workspace-wide features

References

• LSP Specification: https://microsoft.github.io/language-server-protocol/
• rust-analyzer - Rust LSP implementation
• typescript-language-server - TypeScript LSP