get default hr and power zones from config file

CHEATSHEET.md

@@ -129,8 +129,30 @@ incremental: true           # false = re-process everything
 track:
   rdp_epsilon: 0.0001       # GPS simplification — larger = fewer points
   timeseries_hz: 1          # samples/sec in stored JSON (1 = 1 Hz)
+
+athlete:
+  max_hr: 182               # used for context; zones below are authoritative
+  ftp_w: 280                # functional threshold power in watts
+  hr_zones:                 # 5-zone Coggan, explicit bpm boundaries [[lo, hi], ...]
+    - [0,   115]            # Z1 recovery
+    - [115, 137]            # Z2 endurance
+    - [137, 155]            # Z3 tempo
+    - [155, 169]            # Z4 threshold
+    - [169, 999]            # Z5 VO2max
+  power_zones:              # 7-zone Coggan, explicit watt boundaries
+    - [0,   168]            # Z1 active recovery  (< 55% FTP)
+    - [168, 224]            # Z2 endurance        (55–75%)
+    - [224, 266]            # Z3 tempo            (75–90%)
+    - [266, 308]            # Z4 threshold        (90–105%)
+    - [308, 364]            # Z5 VO2max           (105–120%)
+    - [364, 420]            # Z6 anaerobic        (120–150%)
+    - [420, 9999]           # Z7 neuromuscular    (> 150%)
 ```
 
+Zones are written into `index.json` under `owner.athlete` 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 update `index.json`.
+
 ---
 
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