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/app/api/v1/router.py

@@ -0,0 +1,12 @@
+from fastapi import APIRouter
+
+from app.api.v1.endpoints.bootstrap import router as bootstrap_router
+from app.api.v1.endpoints.employees import router as employees_router
+from app.api.v1.endpoints.health import router as health_router
+from app.api.v1.endpoints.reimbursements import router as reimbursements_router
+
+router = APIRouter()
+router.include_router(health_router, tags=["health"])
+router.include_router(bootstrap_router, tags=["bootstrap"])
+router.include_router(employees_router, prefix="/employees", tags=["employees"])
+router.include_router(reimbursements_router, prefix="/reimbursements", tags=["reimbursements"])