v0.13.7 - Distinct blueprint handles

Changes

• Blueprints created implicitly (by globals_save, navigation_items_save, or duplicating a blueprint with the same title) now take the next free handle instead of colliding with an existing one. A handle you pass explicitly is never changed; a collision is a validation error.
• Existing duplicate handles in production were renamed after their owner (for example a second site_settings became settings_shop). The lowest-id blueprint kept the contested handle, so existing lookups resolve as before.