Two related navigation fixes:
1. Back-button now uses real browser history. Sub-view "Tilbake"
buttons (permalink, tag page, personvern, public list) all used
to call goPublicHome() — which always sent the user to / —
instead of returning to wherever they came from. Replaced with
a single backToCallerOrHome() that delegates to
navigate.goBack(fallback), which calls window.history.back() if
there's a prior entry, else navigates to /hjem (or / when
anonymous) so cold-loaded permalinks still have somewhere to go.
2. Cold-load redirect: a logged-in user landing on / probably
wants their own dashboard, not the public marketing surface.
After the me-probe finishes in onMount, if the initial route
was 'public-home' and session.user exists, push to /hjem
instead of applying the public-home route. This only runs on
initial mount (not on every popstate), so browser-back from
/hjem to / still works if the user explicitly navigates there.
The wordmark in the nav also picks its destination by auth state
now — logged-in users go to /hjem, anonymous users to /. Otherwise
clicking it post-redirect would just bounce back to /hjem.