Feature/post entity

[Mimah97]

Add Post entity for creator content

Summary

Introduces a Post entity for creator content with free/paid types, drafts, and media URLs.

Changes

• Post entity: id, creator_id, title, body, type (free|paid), price (nullable), media_urls (JSON array), published_at (nullable), created_at, updated_at
• Relations: ManyToOne to Creator; OneToMany on Creator
• Indexes: (creator_id, published_at) for creator listings; (type) for filtering
• Validation: price null when type=free; price >= 0 when type=paid (enforced in entity hooks)
• PostsModule: Registers Post entity with TypeORM
• Docs: src/posts/README.md describing fields and validation

Behavior

• Draft vs published: Draft when published_at is null; published when set
• media_urls: Stored as JSON array of strings

Acceptance criteria

• Post entity exists and syncs
• Can create post with creator_id, title, body, type, price, media_urls
• Relation to Creator works
• media_urls stores array of URLs
• Draft support (published_at null)
• Price validation for free vs paid
  closes Add Posts/Content module – entity #34