feat: add embedded MCP server and Makefile

Add an MCP (Model Context Protocol) server that starts on 127.0.0.1:9427
at app launch, sharing connection pools with the Tauri IPC layer. This
lets Claude (or any MCP client) query PostgreSQL through Tusk's existing
connections.

MCP tools: list_connections, execute_query, list_schemas, list_tables,
describe_table.

Also add a Makefile with targets for dev, build (cross-platform),
install/uninstall, lint, and formatting.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

src-tauri/src/lib.rs

@@ -1,16 +1,37 @@
 mod commands;
 mod error;
+mod mcp;
 mod models;
 mod state;
 mod utils;
 
 use state::AppState;
+use std::sync::Arc;
+use tauri::Manager;
 
 pub fn run() {
+    let shared_state = Arc::new(AppState::new());
+
     tauri::Builder::default()
         .plugin(tauri_plugin_shell::init())
         .plugin(tauri_plugin_dialog::init())
-        .manage(AppState::new())
+        .manage(shared_state)
+        .setup(|app| {
+            let state = app.state::<Arc<AppState>>().inner().clone();
+            let connections_path = app
+                .path()
+                .app_data_dir()
+                .expect("failed to resolve app data dir")
+                .join("connections.json");
+
+            tokio::spawn(async move {
+                if let Err(e) = mcp::start_mcp_server(state, connections_path, 9427).await {
+                    log::error!("MCP server error: {}", e);
+                }
+            });
+
+            Ok(())
+        })
         .invoke_handler(tauri::generate_handler![
             // connections
             commands::connections::get_connections,