M0: implement operational core

Backend: SQLAlchemy models, Alembic migrations, requirements lockfile. Frontend: pinned deps, package-lock, vite-env types fix. Verified compose build/health, pytest, ruff clean.

backend/app/models/maintenance.py

@@ -0,0 +1,22 @@
+import uuid
+from datetime import datetime
+
+from sqlalchemy import DateTime, ForeignKey, Integer, String, Text
+from sqlalchemy.dialects.postgresql import UUID
+from sqlalchemy.orm import Mapped, mapped_column
+
+from app.core.db import Base
+from app.models.mixins import UUIDPrimaryKeyMixin
+
+
+class MaintenanceRecord(UUIDPrimaryKeyMixin, Base):
+    __tablename__ = "maintenance_records"
+
+    public_ref: Mapped[str] = mapped_column(String(20), unique=True, nullable=False)
+    vehicle_id: Mapped[uuid.UUID] = mapped_column(
+        UUID(as_uuid=True), ForeignKey("vehicles.id"), nullable=False
+    )
+    occurred_at: Mapped[datetime] = mapped_column(DateTime(timezone=True), nullable=False)
+    odometer_km: Mapped[int] = mapped_column(Integer, nullable=False)
+    category: Mapped[str] = mapped_column(String(60), nullable=False)
+    summary: Mapped[str] = mapped_column(Text, nullable=False)