Show decision evidence as a summary row on the card

The evidence for a chat-derived decision was hidden behind a code icon,
objections never appeared, and the Decisions tab had no evidence at all.
The card now shows "1 reason · 1 constraint · 1 objection" under its
options, which opens an Evidence popover with a header and icon close,
rows grouped by option, decision-wide items under "Applies to all
options", labelled supporters, and quoted objections. Objections come
from the existing oppose stances already in client thread state.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>