Previously a signed-in user landing on `/` saw the same page as an
anonymous visitor: the visitor hero, the flagship marketing cards, and
the instance-wide public feed. "Home" should mean "your stuff."
The home route now branches on session: signed-out visitors keep the
marketing + public-feed layout from #303; signed-in users get a
personal dashboard showing their own activities reverse-chronologically
(all visibilities), a welcome line linking to their profile, and a
"New Activity" CTA. The public instance feed and marketing blurbs are
suppressed for signed-in users — they'd be redundant on a personal
landing surface.
Loader picks `listActivities(user.id)` vs `listRecentPublicActivities`
based on session, so only one feed query runs per request.
Updates the `journal-landing` spec with the new session-based split and
a "Personal dashboard for signed-in users" requirement.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
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