chore: update profiles cadence from monthly to weekly, randomized day

Matches the instagram-archiver-posts healthchecks.io check's Simple
Schedule (period + grace, day-agnostic). The disabled systemd timer
now spreads across the whole week (OnCalendar=weekly + 6d randomized
delay) rather than pinning to a fixed day, same "don't look like a
machine" reasoning as the stories timer's 45m jitter -- just applied
to the day instead of the minute.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_011qAds5qr7nZRq5R4yAuxUk

scripts/gdl-cron.sh

@@ -2,7 +2,7 @@
 # Unattended wrapper around gdl-sync.py. One argument: the run mode.
 #
 #   stories     daily      ~6 requests; the only surface that cannot be backfilled
-#   profiles    monthly    every surface, --abort 50: stops enumerating a profile
+#   profiles    weekly     every surface, --abort 50: stops enumerating a profile
 #                          once it reaches content already held, so it costs
 #                          ~40-60 requests and catches everything NEW
 #   full-sweep  rarely     every surface, no abort: walks each profile to the end