feat: add SQLAlchemy database models and tests

Add the data layer for the spending analysis app including models for
household members, accounts, categories, transactions, categorization
rules, and CSV import mappings. All models use SQLAlchemy 2.0 mapped
columns with proper foreign key relationships. Includes db.py with
Base class, engine/session factories, and 6 passing tests.

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

src/models/__init__.py

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+from src.models.household import HouseholdMember
+from src.models.account import Account
+from src.models.category import Category
+from src.models.transaction import Transaction
+from src.models.rule import CategorizationRule
+from src.models.csv_mapping import CsvMapping

src/models/account.py

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+from __future__ import annotations
+
+from typing import TYPE_CHECKING
+
+from sqlalchemy import ForeignKey, String
+from sqlalchemy.orm import Mapped, mapped_column, relationship
+
+from src.db import Base
+
+if TYPE_CHECKING:
+    from src.models.household import HouseholdMember
+
+
+class Account(Base):
+    __tablename__ = "accounts"
+
+    id: Mapped[int] = mapped_column(primary_key=True)
+    name: Mapped[str] = mapped_column(String(100))
+    institution: Mapped[str] = mapped_column(String(100))
+    account_type: Mapped[str] = mapped_column(String(20))
+    owner_id: Mapped[int | None] = mapped_column(ForeignKey("household_members.id"))
+    is_shared: Mapped[bool] = mapped_column(default=False)
+
+    owner: Mapped[HouseholdMember | None] = relationship(back_populates="accounts")

src/models/category.py

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+from sqlalchemy import String
+from sqlalchemy.orm import Mapped, mapped_column
+
+from src.db import Base
+
+
+class Category(Base):
+    __tablename__ = "categories"
+
+    id: Mapped[int] = mapped_column(primary_key=True)
+    name: Mapped[str] = mapped_column(String(100), unique=True)
+    default_tag: Mapped[str | None] = mapped_column(String(20))
+    icon: Mapped[str | None] = mapped_column(String(50))

src/models/csv_mapping.py

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+from __future__ import annotations
+
+from typing import TYPE_CHECKING
+
+from sqlalchemy import ForeignKey, String, Text
+from sqlalchemy.orm import Mapped, mapped_column, relationship
+
+from src.db import Base
+
+if TYPE_CHECKING:
+    from src.models.account import Account
+
+
+class CsvMapping(Base):
+    __tablename__ = "csv_mappings"
+
+    id: Mapped[int] = mapped_column(primary_key=True)
+    name: Mapped[str] = mapped_column(String(100))
+    fingerprint: Mapped[str] = mapped_column(String(500))
+    column_map: Mapped[str] = mapped_column(Text)
+    amount_logic: Mapped[str] = mapped_column(String(50))
+    account_id: Mapped[int] = mapped_column(ForeignKey("accounts.id"))
+
+    account: Mapped[Account] = relationship()

src/models/household.py

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+from __future__ import annotations
+
+from typing import TYPE_CHECKING
+
+from sqlalchemy import String
+from sqlalchemy.orm import Mapped, mapped_column, relationship as sa_relationship
+
+from src.db import Base
+
+if TYPE_CHECKING:
+    from src.models.account import Account
+
+
+class HouseholdMember(Base):
+    __tablename__ = "household_members"
+
+    id: Mapped[int] = mapped_column(primary_key=True)
+    name: Mapped[str] = mapped_column(String(100))
+    relationship: Mapped[str] = mapped_column(String(50))
+
+    accounts: Mapped[list[Account]] = sa_relationship(back_populates="owner")

src/models/rule.py

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+from __future__ import annotations
+
+from typing import TYPE_CHECKING
+
+from sqlalchemy import ForeignKey, String
+from sqlalchemy.orm import Mapped, mapped_column, relationship
+
+from src.db import Base
+
+if TYPE_CHECKING:
+    from src.models.category import Category
+    from src.models.household import HouseholdMember
+
+
+class CategorizationRule(Base):
+    __tablename__ = "categorization_rules"
+
+    id: Mapped[int] = mapped_column(primary_key=True)
+    pattern: Mapped[str] = mapped_column(String(300))
+    category_id: Mapped[int] = mapped_column(ForeignKey("categories.id"))
+    tag_override: Mapped[str | None] = mapped_column(String(20))
+    attributed_to_id: Mapped[int | None] = mapped_column(ForeignKey("household_members.id"))
+    priority: Mapped[int] = mapped_column(default=0)
+
+    category: Mapped[Category] = relationship()
+    attributed_to: Mapped[HouseholdMember | None] = relationship()

src/models/transaction.py

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+from __future__ import annotations
+
+import datetime
+from typing import TYPE_CHECKING
+
+from sqlalchemy import Date, ForeignKey, Numeric, String, Text
+from sqlalchemy.orm import Mapped, mapped_column, relationship
+
+from src.db import Base
+
+if TYPE_CHECKING:
+    from src.models.account import Account
+    from src.models.category import Category
+    from src.models.household import HouseholdMember
+
+
+class Transaction(Base):
+    __tablename__ = "transactions"
+
+    id: Mapped[int] = mapped_column(primary_key=True)
+    date: Mapped[datetime.date] = mapped_column(Date)
+    amount: Mapped[float] = mapped_column(Numeric(10, 2))
+    description: Mapped[str] = mapped_column(String(300))
+    raw_description: Mapped[str | None] = mapped_column(Text)
+    account_id: Mapped[int] = mapped_column(ForeignKey("accounts.id"))
+    category_id: Mapped[int | None] = mapped_column(ForeignKey("categories.id"))
+    attributed_to_id: Mapped[int | None] = mapped_column(ForeignKey("household_members.id"))
+    tag: Mapped[str | None] = mapped_column(String(20))
+    source_category: Mapped[str | None] = mapped_column(String(100))
+    is_transfer: Mapped[bool] = mapped_column(default=False)
+    transfer_pair_id: Mapped[int | None] = mapped_column(ForeignKey("transactions.id"))
+
+    account: Mapped[Account] = relationship()
+    category: Mapped[Category | None] = relationship()
+    attributed_to: Mapped[HouseholdMember | None] = relationship()