feat: add FastAPI backend with PostgreSQL and start script fixes

- Add server/ directory with FastAPI backend
- Fix server/start.sh to properly handle venv on Windows/Git Bash
- Add alembic migrations and pyproject.toml
- Add server tests

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

server/src/x_financial_server.egg-info/requires.txt

@@ -0,0 +1,16 @@
+fastapi<1.0.0,>=0.115.0
+uvicorn[standard]<1.0.0,>=0.30.0
+sqlalchemy<3.0.0,>=2.0.36
+alembic<2.0.0,>=1.14.0
+psycopg[binary]<4.0.0,>=3.2.0
+pydantic-settings<3.0.0,>=2.6.0
+python-dotenv<2.0.0,>=1.0.1
+email-validator<3.0.0,>=2.2.0
+
+[dev]
+pytest<9.0.0,>=8.3.0
+httpx<1.0.0,>=0.28.0
+ruff<1.0.0,>=0.8.0
+
+[redis]
+redis<6.0.0,>=5.2.0