feat: auto-seed PR environments with SEED_ON_DEPLOY flag

Release command now runs migrations + seeds test users when
SEED_ON_DEPLOY=true. Tree seeding runs as a background task
on startup via HTTP API. Everything is idempotent and non-fatal.

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

backend/scripts/release.py

@@ -0,0 +1,53 @@
+#!/usr/bin/env python3
+"""
+Railway release command — runs migrations + optional seed data.
+
+Set SEED_ON_DEPLOY=true in Railway env vars to auto-seed test users
+on PR environments. Seeding is idempotent (skips existing records).
+
+Usage (called by railway.toml releaseCommand):
+  python -m scripts.release
+"""
+
+import asyncio
+import subprocess
+import sys
+
+from app.core.config import settings
+
+
+def run_migrations() -> None:
+    """Run alembic upgrade head."""
+    print("\n[release] Running database migrations...")
+    result = subprocess.run(
+        ["alembic", "upgrade", "head"],
+        capture_output=False,
+    )
+    if result.returncode != 0:
+        print("[release] ERROR: Migrations failed!")
+        sys.exit(1)
+    print("[release] Migrations complete.")
+
+
+async def seed_test_data() -> None:
+    """Seed test users (direct DB, no HTTP needed)."""
+    print("\n[release] Seeding test users...")
+    from scripts.seed_test_users import main as seed_users
+    await seed_users()
+    print("[release] Test users seeded.")
+
+
+def main() -> None:
+    run_migrations()
+
+    if settings.SEED_ON_DEPLOY:
+        print("[release] SEED_ON_DEPLOY=true — seeding test data...")
+        asyncio.run(seed_test_data())
+    else:
+        print("[release] SEED_ON_DEPLOY not set — skipping seed data.")
+
+    print("\n[release] Release complete!")
+
+
+if __name__ == "__main__":
+    main()