Stream heart rate from a strap or watch into the ride and the FIT file

A new HRM client in the BLE crate follows the crate's split: the 0x2A37
decoder is a pure function over bytes (u8/u16 formats, the three-state
sensor-contact field, straps that append energy/RR data), and only the
actor touches the radio. Anything exposing the standard Heart Rate
Service works — a chest strap, or a Garmin watch with Broadcast Heart
Rate on.

A single-slot supervisor in the app owns the link, shaped like the
trainer's and the controller's. It publishes bpm on a watch channel the
session backend stamps onto each tick's telemetry — never over a heart
rate FTMS itself reported, on the same authority rule as the Zwift
cadence merge — and it clears the reading after eight silent seconds,
so a strap taken off records nothing rather than a flatline of the
last real value. From there the existing pipeline does the rest: ride
screen tile, FIT records, avg/max in lap and session.

The device list routes heart-rate rows to the supervisor, keeps the row
alive while connected (a connected monitor stops advertising), and
shows the live bpm as proof data is flowing — a connected-but-silent
monitor otherwise looks exactly like a working one.

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

src-tauri/src/lib.rs

@@ -13,6 +13,7 @@ pub mod controller;
 pub mod derive;
 pub mod devices;
 pub mod events;
+pub mod heart_rate;
 pub mod profile_view;
 pub mod recording;
 pub mod samples;