Migrate data pipeline from SQLite to PostgreSQL + Docker setup

- Add db.py PostgreSQL abstraction layer (connection, upsert, table mgmt)
- Replace sqlite3 with psycopg2 in: live_candle_fetcher, resampler,
  data_fetcher, fetch_history, import_csv, indicators, base_strategy
- Sanitize table names (colons -> underscores) for PostgreSQL compat
- Replace INSERT OR REPLACE with ON CONFLICT upserts
- Replace pandas to_sql() with batch upsert_candles()
- Add scripts: resampler_loop, gap_detector, backup_runner, cron_scheduler
- Add migrate_sqlite_to_pg.py for one-time data migration
- Add Dockerfile, docker-compose.yml, supervisord.conf
- Add postgres/postgresql.conf tuned for 4GB RAM (Synology DS1513+)
- Add .dockerignore, .env.docker.example, secrets template
- Update requirements.txt (psycopg2-binary), .gitignore
- Add MIGRATION_PLAN.md with full plan and todo list

scripts/resampler_loop.py

@@ -0,0 +1,69 @@
+#!/usr/bin/env python3
+"""
+Resampler Loop Wrapper
+
+Runs the Resampler in a continuous loop, executing it once per minute.
+This replaces the schedule-based approach used in main_app.py and is
+designed to run as a supervisord-managed process inside Docker.
+"""
+
+import argparse
+import logging
+import os
+import sys
+import time
+import signal
+
+from logging_utils import setup_logging
+from resampler import Resampler, parse_timeframes
+
+shutdown_requested = False
+
+
+def handle_shutdown(signum, frame):
+    global shutdown_requested
+    shutdown_requested = True
+
+
+def main():
+    parser = argparse.ArgumentParser(description="Run the resampler in a continuous loop.")
+    parser.add_argument("--coins", nargs='+', required=True, help="List of coins to process.")
+    parser.add_argument("--timeframes", nargs='+', required=True, help="List of timeframes to generate.")
+    parser.add_argument("--log-level", default="normal", choices=['off', 'normal', 'debug'])
+    args = parser.parse_args()
+
+    signal.signal(signal.SIGTERM, handle_shutdown)
+    signal.signal(signal.SIGINT, handle_shutdown)
+
+    setup_logging(args.log_level, 'ResamplerLoop')
+
+    timeframes_dict = parse_timeframes(args.timeframes)
+    logging.info(f"Resampler loop started. Coins: {args.coins}, Timeframes: {list(timeframes_dict.keys())}")
+
+    while not shutdown_requested:
+        try:
+            # Pass a copy because Resampler.run() deletes '1m' from the dict
+            timeframes_copy = dict(timeframes_dict)
+            resampler = Resampler(
+                log_level=args.log_level,
+                coins=args.coins,
+                timeframes=timeframes_copy
+            )
+            resampler.run()
+        except Exception as e:
+            logging.error(f"Resampler run failed: {e}")
+
+        if shutdown_requested:
+            break
+
+        # Sleep for 60 seconds, but check shutdown flag every second
+        for _ in range(60):
+            if shutdown_requested:
+                break
+            time.sleep(1)
+
+    logging.info("Resampler loop shutting down.")
+
+
+if __name__ == "__main__":
+    main()