fix(mcp): add required description field for rmcp 0.15.0 compatibility

Implementation struct gained a required description field in rmcp 0.15.0.
Populate it from CARGO_PKG_DESCRIPTION.

Author: bug-ops

crates/mcpls-core/src/mcp/server.rs

@@ -434,6 +434,7 @@ impl ServerHandler for McplsServer {
                 name: "mcpls".to_string(),
                 title: Some("MCPLS - MCP to LSP Bridge".to_string()),
                 version: env!("CARGO_PKG_VERSION").to_string(),
+                description: Some(env!("CARGO_PKG_DESCRIPTION").to_string()),
                 icons: None,
                 website_url: Some("https://github.com/bug-ops/mcpls".to_string()),
             },