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>

requirements.txt

@@ -3,6 +3,7 @@ uvicorn[standard]==0.39.0
 sqlalchemy[asyncio]==2.0.49
 aiosqlite==0.22.1
 asyncpg==0.31.0
+psycopg2-binary==2.9.9
 alembic==1.16.5
 pydantic==2.13.2
 pydantic-settings==2.11.0