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

postgres/postgresql.conf

@@ -0,0 +1,26 @@
+# PostgreSQL configuration tuned for Synology DS1513+ (4GB RAM)
+# Place this file at postgres/postgresql.conf and mount it into the container.
+
+# --- Memory ---
+shared_buffers = 128MB
+effective_cache_size = 512MB
+work_mem = 8MB
+maintenance_work_mem = 64MB
+
+# --- Connections ---
+max_connections = 10
+max_worker_processes = 2
+
+# --- WAL / Checkpointing ---
+wal_buffers = 4MB
+checkpoint_completion_target = 0.9
+max_wal_senders = 3
+
+# --- Network ---
+listen_addresses = '*'
+
+# --- Logging ---
+log_statement = 'none'
+log_duration = off
+log_min_duration_statement = 0
+log_line_prefix = '%t [%p]: [%l-1] user=%u,db=%d,app=%a,client=%h '