v0.3 wallets register with the v0.3 backend, so a site built against the
legacy backend answered every v0.3 sign-in with "User not found". The
v0.3 backend resolves website sign-in by each coin's own key and adopts a
legacy identity on first proof, so it serves both generations.
The v0.3 backend has no social linking. Settings now loads linked accounts
separately and hides that section when they are unavailable, instead of
failing the whole page and taking username editing with it. The public user
count and stats may come from a separate backend via
NEXT_PUBLIC_STATS_API_URL; unset keeps today's behavior.
jwinterm