Show a rating on the beans card

[antonkarliner]

Request (arrived by email, paraphrased)

Show a rating indicator directly on the bean cards in "My Beans", so the
most-liked coffees can be identified at a glance without opening each bean.

Context

Ratings already exist per brew (user_stats.rating, captured on the finish
screen) but are only visible inside a bean's detail screen / brew journey.
The beans list and grid cards currently show name, roaster, origin (or roast
date), a favourite heart, and an amount-left badge — no rating.

Related: #71 asked for per-bean statistics including rating (closed; the yearly
stats cover part of it, nothing per bean). #70 (sort beans by roast date)
shipped, so the sort menu is the natural companion surface for this.

Open questions for triage

• Which rating: the average of the user's own brew ratings for that bag, or the
  user's submitted bean review rating? (Brew averages are far denser — review
  submission is ~5% of eligible sessions.)
• Should sorting by rating come with the badge?