fix(plates): a load-kind pick made from exercise detail is stored

[kurktchiev]

Exercise detail opens the plate-loading editor with no routine config, so the editor's default
comes from the equipment alone. For a body-weight exercise that is "Single stack". A routine that
logs the total instead (bodyweight: false) derives "Off" for its set rows, and they show no plate
line. Tapping the lit "Single stack" to fix that stored nothing: setKind compared the pick with
loadKindFor(null, ctx), got a match, and wrote the stamped null that means "back on the
equipment's". The segment and the rows kept disagreeing, and no tap could settle it.

For body-weight equipment with no config, BarWeightEditor now asks loadKindFor for both
readings of the flag and stores the pick unless it is the default under both. Everything else
keeps the old rule:

• A dumbbell's config-less "Off" is what a dumbbell row derives. Storing it would pin "Off" onto
  the exercise everywhere and override the "Single stack" an added-weight entry derives.
• A barbell is "Per side" either way and still stores nothing for it, as the existing test pins.
• With a config (exercise config, the mid-workout sheet) nothing changes.

Two new tests in sheets.plates.test.jsx, which now has 10, all passing. The body-weight one fails
against the old sheets.jsx; the dumbbell one pins that nothing changes there. No strings change;
check-locales.mjs and check-source-strings.mjs pass.

Overlap: #312 rewrites BarWeightEditor. Its diff drops the load-kind segment and setKind
altogether, so if it merges first this change has nothing to apply to.

🤖 Generated with Claude Code

[DuarteSantos8]

Merged and released in v1.3.10, thanks @kurktchiev!

https://github.com/DuarteSantos8/openGym/releases/tag/v1.3.10