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/pricing.py

@@ -0,0 +1,20 @@
+from datetime import date, datetime
+from decimal import Decimal
+
+from sqlalchemy import Date, DateTime, Numeric, String, func
+from sqlalchemy.orm import Mapped, mapped_column
+
+from app.models.base import Base
+
+
+class PricingConfig(Base):
+    __tablename__ = "pricing_config"
+
+    id: Mapped[int] = mapped_column(primary_key=True)
+    name: Mapped[str] = mapped_column(String(100), default="default")
+    electricity_kwh_eur: Mapped[Decimal] = mapped_column(Numeric(6, 4), default=Decimal("0.30"))
+    printer_watt: Mapped[Decimal] = mapped_column(Numeric(8, 2), default=Decimal("200.00"))
+    hourly_rate_eur: Mapped[Decimal] = mapped_column(Numeric(8, 2), default=Decimal("0.00"))
+    markup_percent: Mapped[Decimal] = mapped_column(Numeric(5, 2), default=Decimal("20.00"))
+    valid_from: Mapped[date] = mapped_column(Date, server_default=func.current_date())
+    created_at: Mapped[datetime] = mapped_column(DateTime, server_default=func.now())