feat(highscores): add SQLite Axum service

Add a small standalone Axum service for the shared anonymous top-ten table.
SQLite keeps the deployment self-contained, while one transaction inserts a
validated name and score and removes entries below the canonical top ten.
Expose a health endpoint and same-origin API, with an nginx proxy block and
run instructions beside the service. Keep the service outside the game crate
so native gameplay persistence remains unchanged.

Test Plan:
- `cargo test --manifest-path highscore-server/Cargo.toml` -- passed (3 tests)
- `cargo clippy --manifest-path highscore-server/Cargo.toml --all-targets --all-features -- -D warnings` -- passed
- `cargo +nightly fmt --manifest-path highscore-server/Cargo.toml -- --check` -- passed
- Live executable health, POST, and GET smoke test -- passed
- `git diff --cached --check` -- passed

tdkpin-rs/highscore-server/Cargo.toml

@@ -0,0 +1,17 @@
+[package]
+name = "tdkpin-highscore-server"
+version = "0.1.0"
+edition = "2024"
+publish = false
+
+[dependencies]
+axum = "0.8"
+rusqlite = { version = "0.37", features = ["bundled"] }
+serde = { version = "1", features = ["derive"] }
+serde_json = "1"
+tokio = { version = "1", features = ["macros", "net", "rt-multi-thread"] }
+
+[dev-dependencies]
+http-body-util = "0.1"
+tempfile = "3"
+tower = { version = "0.5", features = ["util"] }