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/services/reimbursement.py

@@ -0,0 +1,20 @@
+from sqlalchemy.orm import Session
+
+from app.models.reimbursement import ReimbursementRequest
+from app.repositories.reimbursement import ReimbursementRepository
+from app.schemas.reimbursement import ReimbursementCreate
+
+
+class ReimbursementService:
+    def __init__(self, db: Session) -> None:
+        self.repository = ReimbursementRepository(db)
+
+    def list_reimbursements(self) -> list[ReimbursementRequest]:
+        return self.repository.list()
+
+    def get_reimbursement(self, request_id: str) -> ReimbursementRequest | None:
+        return self.repository.get(request_id)
+
+    def create_reimbursement(self, payload: ReimbursementCreate) -> ReimbursementRequest:
+        request = ReimbursementRequest(**payload.model_dump(), status="draft")
+        return self.repository.create(request)