feat: add HeartRateProvider (bpm + HR zone)

Add Sensor and UserProfile permissions to manifest.xml (required for
Toybox.Sensor and Toybox.UserProfile API access; build fails without them).

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

manifest.xml

@@ -20,7 +20,10 @@
             Use "Monkey C: Edit Permissions" from the Visual Studio Code command
             palette to update permissions.
         -->
-        <iq:permissions/>
+        <iq:permissions>
+            <iq:uses-permission id="Sensor"/>
+            <iq:uses-permission id="UserProfile"/>
+        </iq:permissions>
         <!--
             Use "Monkey C: Edit Languages" from the Visual Studio Code command
             palette to edit your compatible language list.

source/HeartRateProvider.mc

@@ -0,0 +1,46 @@
+import Toybox.Lang;
+import Toybox.Sensor;
+import Toybox.UserProfile;
+
+// Wraps the heart-rate sensor and maps the current bpm to a zone (1..5).
+// Returns null bpm when no reading is available (e.g. simulator without data
+// simulation), so the view can show a placeholder.
+class HeartRateProvider {
+    private var _hr as Number?;
+    private var _zones as Array<Number>?;
+
+    public function initialize() {
+        _hr = null;
+        _zones = null;
+    }
+
+    public function onStart() as Void {
+        Sensor.setEnabledSensors([Sensor.SENSOR_HEARTRATE]);
+        Sensor.enableSensorEvents(method(:onSensor));
+        _zones = UserProfile.getHeartRateZones(UserProfile.HR_ZONE_SPORT_GENERIC);
+    }
+
+    public function onStop() as Void {
+        Sensor.enableSensorEvents(null);
+    }
+
+    public function onSensor(info as Sensor.Info) as Void {
+        _hr = info.heartRate;
+    }
+
+    public function getHeartRate() as Number? {
+        return _hr;
+    }
+
+    // Returns 1..5, or 0 if HR/zones unavailable.
+    public function getZone() as Number {
+        if (_hr == null || _zones == null) { return 0; }
+        var z = _zones as Array<Number>;
+        var hr = _hr as Number;
+        // _zones holds 6 boundaries: [z1lo, z2lo, z3lo, z4lo, z5lo, max]
+        for (var i = z.size() - 2; i >= 0; i -= 1) {
+            if (hr >= z[i]) { return i + 1 > 5 ? 5 : i + 1; }
+        }
+        return 1;
+    }
+}