feat: add ListingDecision model and Alembic migration

Add ListingDecision SQLModel entity for tracking user like/dislike
decisions on properties, with unique constraint on (user_id, listing_id,
listing_type) and appropriate indexes.

alembic/versions/d6e7f8a9b0c1_add_listing_decision_table.py

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+"""add listing decision table
+
+Revision ID: d6e7f8a9b0c1
+Revises: c5d6e7f8a9b0
+Create Date: 2026-02-21 12:00:00.000000
+
+"""
+from typing import Sequence, Union
+
+from alembic import op
+import sqlalchemy as sa
+import sqlmodel
+
+
+# revision identifiers, used by Alembic.
+revision: str = 'd6e7f8a9b0c1'
+down_revision: Union[str, None] = 'c5d6e7f8a9b0'
+branch_labels: Union[str, Sequence[str], None] = None
+depends_on: Union[str, Sequence[str], None] = None
+
+
+def upgrade() -> None:
+    """Create listingdecision table."""
+    op.create_table('listingdecision',
+        sa.Column('id', sa.Integer(), nullable=False),
+        sa.Column('user_id', sa.Integer(), nullable=False),
+        sa.Column('listing_id', sa.Integer(), nullable=False),
+        sa.Column('listing_type', sqlmodel.sql.sqltypes.AutoString(), nullable=False),
+        sa.Column('decision', sqlmodel.sql.sqltypes.AutoString(), nullable=False),
+        sa.Column('created_at', sa.DateTime(), nullable=True,
+                  server_default=sa.func.now()),
+        sa.Column('updated_at', sa.DateTime(), nullable=True,
+                  server_default=sa.func.now()),
+        sa.ForeignKeyConstraint(['user_id'], ['user.id']),
+        sa.PrimaryKeyConstraint('id'),
+        sa.UniqueConstraint('user_id', 'listing_id', 'listing_type',
+                            name='uq_decision_user_listing'),
+    )
+    op.create_index(op.f('ix_listingdecision_user_id'),
+                    'listingdecision', ['user_id'], unique=False)
+    op.create_index(op.f('ix_listingdecision_listing_id'),
+                    'listingdecision', ['listing_id'], unique=False)
+
+
+def downgrade() -> None:
+    """Drop listingdecision table."""
+    op.drop_index(op.f('ix_listingdecision_listing_id'),
+                  table_name='listingdecision')
+    op.drop_index(op.f('ix_listingdecision_user_id'),
+                  table_name='listingdecision')
+    op.drop_table('listingdecision')

models/decision.py

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+from datetime import datetime
+
+from sqlmodel import SQLModel, Field
+
+
+class ListingDecision(SQLModel, table=True):
+    id: int | None = Field(default=None, primary_key=True)
+    user_id: int = Field(nullable=False, foreign_key="user.id", index=True)
+    listing_id: int = Field(nullable=False, index=True)
+    listing_type: str = Field(nullable=False)  # "RENT" or "BUY"
+    decision: str = Field(nullable=False)  # "liked" or "disliked"
+    created_at: datetime = Field(default_factory=datetime.utcnow)
+    updated_at: datetime = Field(default_factory=datetime.utcnow)