Scaffold SQLAlchemy models, routers, and Alembic migrations

- app/models/: Printer, Filament, PrintJob, Todo, PricingConfig with full
  SQLAlchemy 2.x mapped columns and relationships
- app/routers/: list + get-by-id endpoints for all five resources
- app/db.py: SQLAlchemy engine + SessionLocal + get_db dependency
- alembic/: env.py reads MYSQL_* env vars; 0001_initial_schema mirrors db.sql
- alembic.ini: script_location configured, URL injected at runtime

Since db.sql already created the tables, stamp the DB before running future
migrations:  alembic stamp head

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

app/models/print_job.py

@@ -0,0 +1,41 @@
+import enum
+from datetime import datetime
+from decimal import Decimal
+
+from sqlalchemy import DateTime, Enum, ForeignKey, Integer, Numeric, String, Text, func
+from sqlalchemy.orm import Mapped, mapped_column, relationship
+
+from app.models.base import Base
+
+
+class JobStatus(enum.Enum):
+    queued = "queued"
+    printing = "printing"
+    done = "done"
+    failed = "failed"
+    cancelled = "cancelled"
+
+
+class PrintJob(Base):
+    __tablename__ = "print_jobs"
+
+    id: Mapped[int] = mapped_column(primary_key=True)
+    printer_id: Mapped[int] = mapped_column(ForeignKey("printers.id"))
+    filament_id: Mapped[int | None] = mapped_column(ForeignKey("filaments.id"))
+    name: Mapped[str] = mapped_column(String(200))
+    file_name: Mapped[str | None] = mapped_column(String(255))
+    status: Mapped[JobStatus] = mapped_column(Enum(JobStatus), default=JobStatus.queued)
+    queue_position: Mapped[int | None] = mapped_column(Integer)
+    started_at: Mapped[datetime | None] = mapped_column(DateTime)
+    finished_at: Mapped[datetime | None] = mapped_column(DateTime)
+    duration_minutes: Mapped[int | None] = mapped_column(Integer)
+    filament_used_g: Mapped[Decimal | None] = mapped_column(Numeric(8, 2))
+    cost_eur: Mapped[Decimal | None] = mapped_column(Numeric(8, 2))
+    notes: Mapped[str | None] = mapped_column(Text)
+    created_at: Mapped[datetime] = mapped_column(DateTime, server_default=func.now())
+    updated_at: Mapped[datetime] = mapped_column(
+        DateTime, server_default=func.now(), onupdate=func.now()
+    )
+
+    printer: Mapped["Printer"] = relationship(back_populates="jobs")
+    filament: Mapped["Filament | None"] = relationship(back_populates="jobs")