fix: collapse meeting-detected notification to single action button

remove redundant "open note" and "not now" buttons plus the global
"dismiss →" link in the notification panel — the ✕ close affordance
already exists, and the join action already routes into the live note.
single provider-agnostic label "join and take notes".

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>