feat(train): weights in pounds too, the person's unit or their region's (ADR 0030, D64)

Every weight is still kept in kilograms. It is shown and entered in the
person's unit, chosen in Your body (Weight in: kg | lb, the profile's
new weightUnit), else the region's: pounds in the US, Liberia and
Myanmar. The entry takes 44 to 880 lb, the same 20 to 400 kg. A weight
left untouched in Your body is saved exactly as it was, not rounded
through pounds. The other figures stay metric.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Signed-off-by: Tizian 「ティツィアーン」 <raisondetredev@pm.me>

docs/adr/0030-halkyon-train.md

@@ -1663,9 +1663,16 @@ Strava. What was found, 27 Oct:
     band's and the zones' figures work from. Health Connect's weight records are read
     in when switched on in its screen (its own permission, asked as the others), each
     record once (its id kept, also after deletion), not Train's own, and not one
-    within 10 minutes and 0.1 kg of a weight entered here. **In kilograms alone**:
-    Train is metric throughout and has no units setting yet; pounds come with one,
-    for every figure at once.
+    within 10 minutes and 0.1 kg of a weight entered here. **In kilograms or pounds**
+    (the developer's call, 4 Nov 2026, weight alone): every weight is kept in
+    kilograms, and shown and entered in the person's unit, *Your body*'s *Weight in*
+    (kg | lb, the profile's `weightUnit`), else their region's (pounds in the US,
+    Liberia and Myanmar, `WeightUnit.ofRegion`, from the app's locale); a pound is
+    0.45359237 kg, the entry's range the same 20 to 400 kg (44 to 880 lb). A weight
+    left untouched in *Your body* is saved as it was, not rounded through pounds.
+    The other figures stay metric; a units setting for all of them would come on
+    its own. A profile saved on Train 0.2.0, which doesn't know the field, loses
+    the unit, and the region's applies again until it is picked anew.
 
 ## Consequences