dream: plan ruff 0.11 → 0.16 upgrade (new rules + markdown format)

[franccesco]

Dream finding 020 (planned upgrade)

Umbrella: #20 | Dream: dream-2026-07-23.1

Ruff 0.16.0 is a large jump from 0.11.13 with:

• Markdown code-block formatting by default
• Many preview/RUF/B/ASYNC/UP rules stabilizing
• 2026 formatter style guide
• pre-commit hook id ruff → ruff-check (currently pinned v0.8.3)

Recommend a dedicated upgrade PR after measuring ruff check/format on this tree, with Markdown opt-in/out decision.

Nothing auto-merges.