Render recipe and step times as hours and minutes - #4810

This is #4785 redone the way you asked: no user preference, the times are simply shown in a
human readable format.

While I like the feature I think its a lot more complex than it need to be. I do not think we
need the user preference. Just show the times in a human readable format.

The preference is gone entirely — UserPreference.use_readable_time, its migration, the
serializer entry, the Cosmetic settings checkbox and the regenerated client models are all out.
This pull request touches no Python at all. Six files, all under vue3/, and the formatting is
unconditional.

I have left the duration-field conversion alone. It is a much bigger change than this one, it
breaks the API for existing clients, and it sounded like something you may want to shape
yourself.

What this does

Recipe and step durations are stored and displayed as a flat number of minutes, so a 72 hour
sourdough proof renders as 4320 min, the step timer button shows a bare 4320, and the recipe
card's time chip shows working + waiting summed with no unit at all.

A shared formatter in vue3/src/utils/duration_utils.ts converts minutes for display:

Below an hour it stays minutes; from an hour up it renders H h, plus M min when there is a
remainder. No day rollover — 4320 stays 72 h, matching the table in #382. Timer.vue already
expresses "+3 Days" for the one case where a calendar day matters, and long proofs are spoken as
"72 hours", not "3 days".

Unit labels are passed in by the caller from translation keys, so no unit string is inlined in
the conversion logic. min already existed; h is new in en.json. English keys only, per
docs/contribute/translations.md — Weblate can take it from there.

Applied at the read-only duration displays: both RecipeView layouts, the RecipeCard time
chip, and the StepView timer button. Duration inputs keep plain minutes — entering durations
was never the problem, reading them is. It also removes two hardcoded min strings in
RecipeView.vue that bypassed i18n; they sat on the lines this rewrites.

Notes

• Verified locally: yarn build and the full Python suite on a tree carrying this change.
• I left the surrounding reformatting alone rather than dragging unrelated churn into the diff —
  the files this touches do not currently satisfy the repo's prettier config either way. Happy to
  run it if you would prefer.

Closes #382.