feat: add MarketPlace model, migration, and market_url_for helper

Introduces per-page markets (Phase 2):
- MarketPlace model with soft-delete and unique slug index
- NavTop gains market_id FK to scope nav hierarchy per market
- Migration with backfill creates default 'suma-market' for existing market page
- market_url_for() cross-app URL helper

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

alembic/versions/b2c3d4e5f6a7_add_market_places_table.py

@@ -0,0 +1,97 @@
+"""add market_places table and nav_tops.market_id
+
+Revision ID: b2c3d4e5f6a7
+Revises: a1b2c3d4e5f6
+Create Date: 2026-02-10
+"""
+from alembic import op
+import sqlalchemy as sa
+from sqlalchemy import text
+
+revision = 'b2c3d4e5f6a7'
+down_revision = 'a1b2c3d4e5f6'
+branch_labels = None
+depends_on = None
+
+
+def upgrade() -> None:
+    # 1. Create market_places table
+    op.create_table(
+        'market_places',
+        sa.Column('id', sa.Integer(), autoincrement=True, nullable=False),
+        sa.Column('post_id', sa.Integer(), nullable=False),
+        sa.Column('name', sa.String(255), nullable=False),
+        sa.Column('slug', sa.String(255), nullable=False),
+        sa.Column('description', sa.Text(), nullable=True),
+        sa.Column('created_at', sa.DateTime(timezone=True), server_default=sa.func.now(), nullable=False),
+        sa.Column('updated_at', sa.DateTime(timezone=True), server_default=sa.func.now(), nullable=False),
+        sa.Column('deleted_at', sa.DateTime(timezone=True), nullable=True),
+        sa.ForeignKeyConstraint(['post_id'], ['posts.id'], ondelete='CASCADE'),
+        sa.PrimaryKeyConstraint('id'),
+    )
+    op.create_index('ix_market_places_post_id', 'market_places', ['post_id'])
+    op.create_index(
+        'ux_market_places_slug_active',
+        'market_places',
+        [sa.text('lower(slug)')],
+        unique=True,
+        postgresql_where=sa.text('deleted_at IS NULL'),
+    )
+
+    # 2. Add market_id column to nav_tops
+    op.add_column(
+        'nav_tops',
+        sa.Column('market_id', sa.Integer(), nullable=True),
+    )
+    op.create_foreign_key(
+        'fk_nav_tops_market_id',
+        'nav_tops',
+        'market_places',
+        ['market_id'],
+        ['id'],
+        ondelete='SET NULL',
+    )
+    op.create_index('ix_nav_tops_market_id', 'nav_tops', ['market_id'])
+
+    # 3. Backfill: create default MarketPlace for the 'market' page
+    conn = op.get_bind()
+
+    # Find the market page
+    result = conn.execute(text("""
+        SELECT id FROM posts
+        WHERE slug = 'market' AND is_page = true AND deleted_at IS NULL
+        LIMIT 1
+    """))
+    row = result.fetchone()
+    if row:
+        post_id = row[0]
+
+        # Insert the default market
+        conn.execute(text("""
+            INSERT INTO market_places (post_id, name, slug, created_at, updated_at)
+            VALUES (:post_id, 'Suma Market', 'suma-market', now(), now())
+        """), {"post_id": post_id})
+
+        # Get the new market_places id
+        market_row = conn.execute(text("""
+            SELECT id FROM market_places
+            WHERE slug = 'suma-market' AND deleted_at IS NULL
+            LIMIT 1
+        """)).fetchone()
+
+        if market_row:
+            market_id = market_row[0]
+            # Assign all active nav_tops to this market
+            conn.execute(text("""
+                UPDATE nav_tops SET market_id = :market_id
+                WHERE deleted_at IS NULL
+            """), {"market_id": market_id})
+
+
+def downgrade() -> None:
+    op.drop_index('ix_nav_tops_market_id', table_name='nav_tops')
+    op.drop_constraint('fk_nav_tops_market_id', 'nav_tops', type_='foreignkey')
+    op.drop_column('nav_tops', 'market_id')
+    op.drop_index('ux_market_places_slug_active', table_name='market_places')
+    op.drop_index('ix_market_places_post_id', table_name='market_places')
+    op.drop_table('market_places')