You are working in my existing renewal assistant project.

Please create a new Python script at:

    campaigns/send_appt_reminders.py

that does the following, reusing the existing patterns and utils in this repo:

1. Imports:
   - Use the existing Supabase helper from utils.tools:
       from utils.tools import get_client, log_message
   - Also import:
       from datetime import datetime, timezone
       import argparse
       import pytz (if already used elsewhere; if not, you can skip timezone logic and just use UTC now)

2. Purpose:
   - This script sends **appointment reminder** messages for upcoming renewal appointments.
   - It should read from the existing view **v_appt_reminders** in Supabase.
   - v_appt_reminders already contains only appointments that:
       - are in an appropriate status (e.g. 'new' / 'confirmed')
       - are due a reminder
       - have reminder_sent_at IS NULL
   - For each row returned, send one WhatsApp reminder using the **reply_template** with slug='appt_reminder'.

3. CLI interface:
   - Use argparse with:
       --channel (default: "whatsapp")
       --limit (default: 50)
       --dry-run (flag; if present, do NOT write to DB, just print what would happen)
   - Example usage:
       python campaigns/send_appt_reminders.py
       python campaigns/send_appt_reminders.py --limit 20
       python campaigns/send_appt_reminders.py --dry-run

4. Loading the template:
   - Query the table reply_template to get the row where:
       slug = 'appt_reminder'
       AND channel = <channel argument>
       AND active = true
   - If no template is found, print a clear error and exit with non-zero code.

5. Querying reminders:
   - From v_appt_reminders select up to <limit> rows, ordered by preferred_date, then created_at.
   - Columns you can expect from v_appt_reminders (based on our schema):
       appt_id
       agreement_id (if present)
       agreement_number
       first_name
       last_name
       make
       model
       registration
       channel
       preferred_date
       preferred_time
       status
       reminder_sent_at
       reminder_channel
       tco_token
       tco_completed_at

6. Rendering the message:
   - Take the template body from reply_template.body.
   - Do simple string replacements for:
       {{first_name}}      -> row["first_name"] or ""
       {{centre_name}}     -> "Lincoln Audi" (hard-code for now)
       {{model}}           -> row["model"] or "Audi"
   - Leave any other {{...}} placeholders unchanged if they exist.

7. Logging the outbound message:
   - For each reminder to send, call log_message with:
       agreement_ref   = row["agreement_number"]
       channel         = channel argument (e.g. "whatsapp")
       direction       = "outbound"
       message_text    = final rendered message
       intent_label    = "appt_reminder"
       template_slug   = "appt_reminder"
       source          = "ai"
       model           = None
   - Respect the --dry-run flag:
       - If --dry-run is set, DO NOT call log_message.
       - Instead, just print a preview line like:
         [DRY RUN] Would send reminder for AGREEMENT_NUMBER: "MESSAGE..."

8. Updating appointment_request:
   - For real sends (no --dry-run):
       - Update appointment_request where id = appt_id:
           reminder_sent_at = now() (UTC)
           reminder_channel  = channel argument (e.g. "whatsapp")
       - Use the Supabase Python client from get_client() to perform this update.
       - If an update fails for one row, log an error but continue with others.

9. Output / summary:
   - At the start, print a header:
       "APPOINTMENT REMINDER SENDER"
   - For each processed row, print:
       - Agreement number
       - First name
       - Preferred_date
       - Whether it was sent or dry-run
   - At the end, print a summary:
       - Total reminders considered
       - Total actually sent
       - Total skipped (if any)
       - If dry-run, clearly mark that nothing was written.

10. Code style:
   - Follow the same style as the existing campaigns/send_campaign_batch.py file in this repo:
       - main() function
       - if __name__ == "__main__": main()
       - Clear prints, graceful error handling.

When you’ve created campaigns/send_appt_reminders.py, please run:

    python campaigns/send_appt_reminders.py --dry-run --limit 10

and show me the console output so I can check it.