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>

ui/src/components/ConnectionScreen.svelte

@@ -140,6 +140,28 @@
                   : ''}
               </span>
             </span>
+          {:else if device.kind === 'heartRate'}
+            <!-- The live reading is the row's proof that data is flowing: a
+                 monitor that is connected but silent looks exactly like a
+                 working one otherwise. -->
+            <span class="state">
+              <span class="label">Heart rate</span>
+              <span
+                class="value"
+                class:tone-ok={device.heartRateBpm != null}
+                class:tone-idle={device.heartRateBpm == null}
+              >
+                <span class="dot"></span>{device.heartRateBpm != null
+                  ? `${device.heartRateBpm} bpm`
+                  : '—'}
+              </span>
+            </span>
+            {#if device.batteryPct != null}
+              <span class="state">
+                <span class="label">Battery</span>
+                <span class="value tone-idle"><span class="dot"></span>{device.batteryPct}%</span>
+              </span>
+            {/if}
           {:else if device.batteryPct != null}
             <span class="state">
               <span class="label">Battery</span>
@@ -173,7 +195,10 @@
         <ul>
           <li><strong>Trainer</strong> — turn the pedals for a few seconds.</li>
           <li><strong>Zwift Click</strong> — press any button on the pod.</li>
-          <li><strong>Heart rate strap</strong> — wet the contacts and put it on.</li>
+          <li>
+            <strong>Heart rate</strong> — wet a strap's contacts and put it on; on a sports watch,
+            switch on <em>Broadcast Heart Rate</em>.
+          </li>
         </ul>
         <p class="quiet">
           They will appear here as soon as they advertise. Scanning continues in the background.

ui/src/lib/types.ts

@@ -252,6 +252,8 @@ export interface DeviceInfo {
   services: string[];
   remembered: boolean;
   batteryPct: number | null;
+  /** Live reading from a connected heart rate monitor — proof data is flowing. */
+  heartRateBpm: number | null;
   error: string | null;
 }