Prepare for an eventual frontend

Move the backend code into a backend/ directory, and create a frontend/
directory containing an empty sveltekit project.

Cargo.toml

@@ -1,22 +0,0 @@
-[package]
-name = "city_portal"
-version = "0.1.0"
-edition = "2024"
-
-[dependencies]
-tokio = { version = "1", features = ["full"] }
-axum = "0.8"
-async-graphql = "7"
-async-graphql-axum = "7"
-serde = "1"
-serde_json = "1"
-sqlx = { version = "0.8", features = [
-    "runtime-tokio",
-    "tls-rustls-aws-lc-rs",
-    "postgres",
-    "chrono",
-    "json"
-] }
-chrono = "0.4"
-dotenv = "0.15.0"
-anyhow = "1.0"