Adds the notifications system end-to-end (4 types, payload-versioned
JSONB, SSE-based live unread badge, /notifications page, mark-read API,
fan-out job for activity_published, daily 90-day retention purge).
Bell icon in the navbar with unread badge.
Side-findings from exercising the change:
- Add 6-digit magic code to registration (mirrors login UX, mobile
paste-friendly), with `[Register Magic Link]` console line in dev so
the code is reachable without a real email transport.
- Manual passkey/magic-link toggle on the register form (login already
had it).
- Restrict ALPN to http/1.1 in HTTPS dev so React Router's
singleFetchAction CSRF check (Origin vs. Host) passes — Node doesn't
synthesize Host from h2's :authority. Plain HTTP dev unaffected.
- Followers/Following routes now use the locked-account rule from the
profile route (owner + accepted followers see the list; others 404).
Profile page renders the count chips as plain spans for viewers who
can't see the lists, so private profiles don't surface dead links.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
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