get default hr and power zones from config file

README.md

@@ -133,8 +133,31 @@ track:
   timeseries_hz: 1        # data samples per second stored in JSON
 
 incremental: true         # skip files whose hash hasn't changed
+
+# Optional: athlete profile for zone overlays on HR/power charts
+athlete:
+  max_hr: 182
+  ftp_w: 280
+  hr_zones:               # [[lo, hi], ...] in bpm — 5-zone Coggan
+    - [0,   115]
+    - [115, 137]
+    - [137, 155]
+    - [155, 169]
+    - [169, 999]
+  power_zones:            # [[lo, hi], ...] in watts — 7-zone Coggan
+    - [0,   168]
+    - [168, 224]
+    - [224, 266]
+    - [266, 308]
+    - [308, 364]
+    - [364, 420]
+    - [420, 9999]
 ```
 
+Zones are written into `index.json` at extract time and displayed as overlays on
+HR and Power histograms in the activity detail page. After changing zones, re-run
+`uv run bincio extract` to regenerate `index.json`.
+
 ### Privacy levels
 
 | Level | GPS track | Stats | Appears in index |