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/Cargo.toml

@@ -30,3 +30,7 @@ csv = "1"
 log = "0.4"
 hex = "0.4"
 bigdecimal = { version = "0.4", features = ["serde"] }
+rmcp = { version = "0.15", features = ["server", "macros", "transport-streamable-http-server"] }
+axum = "0.8"
+schemars = "1"
+tokio-util = "0.7"