feat(db): add MonthState enum and lifecycle columns

state defaults to 'planning' (server default plus SQLAlchemy default).
activated_at and closed_at are nullable timestamps that record when
the month crossed each boundary. Alembic batch_alter_table handles
the SQLite rewrite. MonthState is a Python string enum mapped to a
non-native VARCHAR(16).

Refs #15

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

alembic/versions/a4ec4f8f6e9f_add_month_lifecycle_state.py

@@ -0,0 +1,40 @@
+"""add month lifecycle state
+
+Revision ID: a4ec4f8f6e9f
+Revises: ec804bdf366d
+Create Date: 2026-04-17 12:59:25.811354
+
+"""
+from typing import Sequence, Union
+
+from alembic import op
+import sqlalchemy as sa
+
+
+# revision identifiers, used by Alembic.
+revision: str = 'a4ec4f8f6e9f'
+down_revision: Union[str, Sequence[str], None] = 'ec804bdf366d'
+branch_labels: Union[str, Sequence[str], None] = None
+depends_on: Union[str, Sequence[str], None] = None
+
+
+def upgrade() -> None:
+    """Upgrade schema."""
+    # ### commands auto generated by Alembic - please adjust! ###
+    with op.batch_alter_table('month', schema=None) as batch_op:
+        batch_op.add_column(sa.Column('state', sa.Enum('planning', 'active', 'closed', name='monthstate', native_enum=False, length=16), server_default='planning', nullable=False))
+        batch_op.add_column(sa.Column('activated_at', sa.DateTime(timezone=True), nullable=True))
+        batch_op.add_column(sa.Column('closed_at', sa.DateTime(timezone=True), nullable=True))
+
+    # ### end Alembic commands ###
+
+
+def downgrade() -> None:
+    """Downgrade schema."""
+    # ### commands auto generated by Alembic - please adjust! ###
+    with op.batch_alter_table('month', schema=None) as batch_op:
+        batch_op.drop_column('closed_at')
+        batch_op.drop_column('activated_at')
+        batch_op.drop_column('state')
+
+    # ### end Alembic commands ###

src/quartermaster/models.py

@@ -27,6 +27,12 @@ class Section(str, enum.Enum):
     sinking_fund = "sinking_fund"
 
 
+class MonthState(str, enum.Enum):
+    planning = "planning"
+    active = "active"
+    closed = "closed"
+
+
 SECTION_LABELS: dict[Section, str] = {
     Section.income: "Incomes",
     Section.fixed_bill: "Fixed Amount Bills",
@@ -86,6 +92,18 @@ class Month(Base):
 
     id: Mapped[int] = mapped_column(primary_key=True)
     year_month: Mapped[str] = mapped_column(String(7), nullable=False, unique=True)
+    state: Mapped[MonthState] = mapped_column(
+        Enum(MonthState, native_enum=False, length=16),
+        nullable=False,
+        default=MonthState.planning,
+        server_default=MonthState.planning.value,
+    )
+    activated_at: Mapped[datetime | None] = mapped_column(
+        DateTime(timezone=True), nullable=True
+    )
+    closed_at: Mapped[datetime | None] = mapped_column(
+        DateTime(timezone=True), nullable=True
+    )
     created_at: Mapped[datetime] = mapped_column(
         DateTime(timezone=True), server_default=func.now(), nullable=False
     )