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/core/src/lib.rs

@@ -0,0 +1,17 @@
+//! Pure ride logic: physics, profiles, GPX import and session state.
+//!
+//! This crate has no I/O and no platform dependencies (NFR-5). Everything here
+//! is unit-testable with synthetic telemetry, and it must stay that way — BLE
+//! lives in `bikecontrol-ble`, file writing in `bikecontrol-fit`.
+
+pub mod gpx;
+pub mod physics;
+pub mod profile;
+pub mod session;
+pub mod types;
+
+pub use profile::{Block, Channel, Extent, Profile, Segment, Waveform};
+pub use session::{RideSession, SessionEvent};
+pub use types::{
+    ConnectionState, ControlMode, ControlTarget, RideSnapshot, RiderConfig, SafetyLimits, Telemetry,
+};