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

docs/gallery-dl.md

@@ -358,7 +358,7 @@ means an infrequent full sync costs barely more than a frequent one, because it
 only fetches what is new.
 
 ```
-# monthly, everything
+# weekly, everything
 gdl-sync.py --index <viewer-url> --staging ~/gdl/staging \
     --publish <user>@<nas>:<archives> --archive-db ~/gdl/artms.db \
     --urls-file artms_account_links.txt --execute