feat(lsp): implement LSP client and server management

- Added LspClient for handling communication with LSP servers, including methods for initialization, notifications, and requests.
- Introduced LspManager to manage multiple LSP server connections, allowing for connection, disconnection, and retrieval of server capabilities.
- Created tools for connecting to LSP servers, retrieving diagnostics, hover information, code completion, definitions, and references.
- Enhanced UI rendering to display token usage and settings in the overlay.
- Updated status bar to show current token usage and selected provider/model.

src/app/mod.rs

@@ -1,5 +1,6 @@
 //! Top-level application module: harness, modes, runtime loop, state,
-//! workflows, subagents, review, background bash, and MCP integration.
+//! workflows, subagents, review, background bash, MCP integration, and
+//! native LSP client.
 pub mod harness;
 pub mod mode;
 pub mod runtime;
@@ -9,3 +10,4 @@ pub mod subagent;
 pub mod review;
 pub mod bgbash;
 pub mod mcp;
+pub mod lsp;