Add /app/today redirect route to most recent journal day
Completes the partial M1 fix — /app/transcripts/ already redirects to
the most recent day with data, but /app/today was still a 404. Added
to the root blueprint since /app/today is a top-level convenience URL,
not scoped to the transcripts app prefix.
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>