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/commands/queries.rs

@@ -4,6 +4,7 @@ use crate::state::AppState;
 use serde_json::Value;
 use sqlx::postgres::PgRow;
 use sqlx::{Column, Row, TypeInfo};
+use std::sync::Arc;
 use std::time::Instant;
 use tauri::State;
 
@@ -68,18 +69,17 @@ pub fn pg_value_to_json(row: &PgRow, index: usize) -> Value {
     }
 }
 
-#[tauri::command]
-pub async fn execute_query(
-    state: State<'_, AppState>,
-    connection_id: String,
-    sql: String,
+pub async fn execute_query_core(
+    state: &AppState,
+    connection_id: &str,
+    sql: &str,
 ) -> TuskResult<QueryResult> {
-    let read_only = state.is_read_only(&connection_id).await;
+    let read_only = state.is_read_only(connection_id).await;
 
     let pools = state.pools.read().await;
     let pool = pools
-        .get(&connection_id)
-        .ok_or(TuskError::NotConnected(connection_id))?;
+        .get(connection_id)
+        .ok_or_else(|| TuskError::NotConnected(connection_id.to_string()))?;
 
     let start = Instant::now();
     let rows = if read_only {
@@ -88,14 +88,14 @@ pub async fn execute_query(
             .execute(&mut *tx)
             .await
             .map_err(TuskError::Database)?;
-        let result = sqlx::query(&sql)
+        let result = sqlx::query(sql)
             .fetch_all(&mut *tx)
             .await
             .map_err(TuskError::Database);
         tx.rollback().await.map_err(TuskError::Database)?;
         result?
     } else {
-        sqlx::query(&sql)
+        sqlx::query(sql)
             .fetch_all(pool)
             .await
             .map_err(TuskError::Database)?
@@ -127,3 +127,12 @@ pub async fn execute_query(
         execution_time_ms,
     })
 }
+
+#[tauri::command]
+pub async fn execute_query(
+    state: State<'_, Arc<AppState>>,
+    connection_id: String,
+    sql: String,
+) -> TuskResult<QueryResult> {
+    execute_query_core(&state, &connection_id, &sql).await
+}