fix(image): keep the Tor onion reachable on RTC-less boards

An RTC-less Pi boots at 1970; Tor then rejects the consensus and the unlock
onion never publishes. Bake a clock floor (build epoch) into the initramfs and
jump the clock forward to it before Tor starts, and pass a numeric tor_ntp= in
the cmdline so busybox ntpd syncs without DNS. Proven on hardware: the onion
unlock succeeded on a Pi 3 after this.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

lim/configuration/initramfs-tools/tor_hook

@@ -25,6 +25,8 @@ for bb in /bin/busybox /usr/bin/busybox; do
     [ -x "$bb" ] && { copy_exec "$bb" /usr/local/bin/busybox; break; }
 done
 
+date -u +%s > "${DESTDIR}/etc/tor-clock-floor"
+
 # Onion keys + torrc, staged on the system by lim.
 mkdir -p "${DESTDIR}/etc/tor/onion"
 for key in hostname hs_ed25519_public_key hs_ed25519_secret_key; do