Add the yaak.run playground API (#681)

crates-server/yaak-playground/Cargo.toml

@@ -0,0 +1,25 @@
+[package]
+name = "yaak-playground"
+version = "0.1.0"
+edition = "2024"
+publish = false
+description = "A small, disposable API for trying Yaak against (yaak.run)"
+
+[[bin]]
+name = "yaak-playground"
+path = "src/main.rs"
+
+[dependencies]
+axum = "0.7"
+bytes = "1.11.1"
+clap = { version = "4.5", features = ["derive", "env"] }
+env_logger = "0.11"
+log = { workspace = true }
+serde = { workspace = true, features = ["derive"] }
+serde_json = { workspace = true }
+tokio = { workspace = true, features = ["rt-multi-thread", "macros", "signal", "net"] }
+tower-http = { version = "0.6", features = ["cors"] }
+uuid = { version = "1", features = ["v4"] }
+
+[dev-dependencies]
+tower = { version = "0.5", features = ["util"] }