On a transient error (network blip, DNS not ready, homeserver 5xx) a
secondary account's bring-up was immediately skipped for the entire
daemon lifetime. This bit janet's catgirl account repeatedly when the
host DNS resolver wasn't ready at daemon start — the account would
silently disappear until the next restart.
Add a PermanentBringUpError sentinel in client.rs so callers can
distinguish M_UNKNOWN_TOKEN (stale/expired token — permanent, don't
retry) from transient network/homeserver errors.
In main.rs, replace the immediate skip with a bounded retry loop for
secondary accounts: up to 4 attempts with 2s/5s/15s/30s backoffs
(~52s total wait). On a transient error the daemon now stays alive
serving the primary and any other healthy accounts while the failing
secondary gets another chance. Permanent failures (PermanentBringUpError)
still skip immediately with no retry.
The primary account keep its existing behaviour: fatal on non-permanent
error so systemd restarts the whole daemon (systemd is the right retry
mechanism for primary bring-up failure).
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