MAINT-20 part 1: peakguard.py keeps the reference-pack sentence a test pins

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

goodwe_controller/app/peakguard.py

@@ -32,8 +32,9 @@ SOURCE = "peak"
 # test_peakguard.py.
 # Not a read: `decide()` takes them as arguments.
 PEAK_OPTION_DEFAULTS = {
-    # Percent a forced discharge may not go below; see
-    # DECISIONS/SAFETY-07-peak-guard.md.
+    # Percent a forced discharge may not go below. 20 is derived from the
+    # reference pack, 300 Ah at 51.2 V with DoD 90 - 13.8 kWh usable (a test
+    # pins this wording). See DECISIONS/SAFETY-07-peak-guard.md.
     "peak_soc_floor": 20,
     # The pack's own cut-out in percent; rule 8 of validate.py refuses a
     # `peak_soc_floor` at or below it.