Bets are proposed from the owner's notes as well as open issues, once the bets planner is on main #8825

Replaces #8807. Both builders declined, correctly: it extends src/actions/bets.ts, which is only in pull #8771 for #8713, not on main. This issue waits for #8713 to land.

Done looks like:

• [ ] The bets planner reads the owner's notes (from #8696, on main) beside open issues, groups both by theme rather than by first label only, and proposes bets from the groups.
• [ ] A note with no issue behind it can seed a proposed bet, named as from that note.
• [ ] A test seeds one note and two unrelated issues and finds a bet seeded by the note. A note another person wrote is never read.

Files: src/actions/bets.ts, test/bets.test.ts, docs/features/bets.md (all from #8713) Risks: privacy. Notes are the owner's; read them only for the owner's own repositories.