Scaffold workspace, shared types and requirements spec

Cargo workspace with core/ble/fit/probe crates. crates/core/src/types.rs
is the fixed contract between the BLE layer, ride engine and UI.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

crates/probe/Cargo.toml

@@ -0,0 +1,20 @@
+[package]
+name = "bikecontrol-probe"
+version.workspace = true
+edition.workspace = true
+license.workspace = true
+
+[[bin]]
+name = "probe"
+path = "src/main.rs"
+
+[dependencies]
+bikecontrol-core = { workspace = true }
+bikecontrol-ble = { workspace = true }
+btleplug = { workspace = true }
+tokio = { workspace = true, features = ["full"] }
+futures = { workspace = true }
+uuid = { workspace = true }
+anyhow = { workspace = true }
+tracing = { workspace = true }
+tracing-subscriber = { workspace = true }