app/views/brands/index.html.erb: Hide owner, show and edit.
List products in brand page.
app/views/brands/edit.html.erb: Disable edit name and slug.
Add listing brands page for users which not signed in.
Add link to brand's website from brands list page.
app/models/brand.rb: Validates uniqueness of name and slug.
app/models/product.rb: Validates uniqueness of slug.
Add index to name and slug, it are unique.
Add index to slug of product, it's unique.
db/schema.rb: Update(by migration).
After sign in, jump to /brands/.