feat: auto-migrate SQLite data to Postgres on first deploy

- Add trumpsignal.db to git (one-time migration source)
- entrypoint.sh detects empty Postgres and runs migration automatically
- scripts/migrate_sqlite_to_postgres.py: posts, subscriptions, bot_trades
- Add psycopg2-binary to requirements for migration script

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

.dockerignore

@@ -3,7 +3,6 @@ __pycache__/
 *.pyc
 *.pyo
 .env
-*.db
 *.db-shm
 *.db-wal
 .git/
@@ -11,4 +10,3 @@ __pycache__/
 *.md
 test_*.py
 simulate_trades.py
-scripts/