Consolidated migration for the Publishing module.

Creates all 4 publishing tables in their V2 state. Every statement uses IF NOT EXISTS / IF NOT NULL guards so it is safe to run even when the tables already exist (e.g. created by PhoenixKit core migrations).

Tables

• phoenix_kit_publishing_groups — content groups (blog, faq, docs, …)
• phoenix_kit_publishing_posts — routing shell (slug/date identity + active version pointer)
• phoenix_kit_publishing_versions — source of truth (status, published_at, metadata)
• phoenix_kit_publishing_contents — per-language content (title + body, with override columns for future use)

Design

• UUID v7 primary keys (uuid_generate_v7() default)
• JSONB data column on versions and contents for extensibility
• All timestamps use timestamptz
• Slug is nullable (timestamp-mode posts use date/time instead)
• User FK columns (created_by_uuid, updated_by_uuid) reference phoenix_kit_users(uuid) when that table exists; otherwise skipped.