feat(route-sections): add dynamic route sections

Replace hardcoded homepage featured route groups with a fully managed dynamic system:
- add database models RouteSection and RouteSectionProduct for storing route groups and their associated products
- create Alembic migration 0004_route_sections for the new tables
- extend SiteConfigPatchIn schema with subtitle and productIds fields
- refactor shared site_config utility to load dynamic route sections instead of fixed groups
- implement admin CRUD API with validation for duplicate/conflicting product associations
- update public and admin API documentation to reflect the new system
- add default route section seed data and comprehensive test coverage

alembic/versions/0004_route_sections.py

@@ -0,0 +1,54 @@
+"""Add route section configuration.
+
+Revision ID: 0004_route_sections
+Revises: 0003_campaign_display_fields
+Create Date: 2026-07-02
+"""
+
+from alembic import op
+import sqlalchemy as sa
+from sqlalchemy import inspect
+
+
+revision = "0004_route_sections"
+down_revision = "0003_campaign_display_fields"
+branch_labels = None
+depends_on = None
+
+
+def upgrade() -> None:
+    bind = op.get_bind()
+    existing_tables = set(inspect(bind).get_table_names())
+
+    if "RouteSection" not in existing_tables:
+        op.create_table(
+            "RouteSection",
+            sa.Column("id", sa.String(), nullable=False),
+            sa.Column("title", sa.String(), nullable=False),
+            sa.Column("subtitle", sa.Text(), nullable=True),
+            sa.Column("sortOrder", sa.Integer(), nullable=False, server_default="0"),
+            sa.Column("isActive", sa.Boolean(), nullable=False, server_default=sa.true()),
+            sa.Column("createdAt", sa.DateTime(), nullable=False),
+            sa.Column("updatedAt", sa.DateTime(), nullable=False),
+            sa.PrimaryKeyConstraint("id"),
+        )
+
+    if "RouteSectionProduct" not in existing_tables:
+        op.create_table(
+            "RouteSectionProduct",
+            sa.Column("sectionId", sa.String(), nullable=False),
+            sa.Column("productId", sa.String(), nullable=False),
+            sa.Column("sortOrder", sa.Integer(), nullable=False, server_default="0"),
+            sa.ForeignKeyConstraint(["productId"], ["Product.id"], ondelete="CASCADE"),
+            sa.ForeignKeyConstraint(["sectionId"], ["RouteSection.id"], ondelete="CASCADE"),
+            sa.PrimaryKeyConstraint("sectionId", "productId"),
+        )
+
+
+def downgrade() -> None:
+    bind = op.get_bind()
+    existing_tables = set(inspect(bind).get_table_names())
+    if "RouteSectionProduct" in existing_tables:
+        op.drop_table("RouteSectionProduct")
+    if "RouteSection" in existing_tables:
+        op.drop_table("RouteSection")