Phase 0+1: native post writes, Ghost no longer write-primary

- Final sync script with HTML verification + author→user migration
- Make ghost_id nullable on posts/authors/tags, add UUID/timestamp defaults
- Add user profile fields (bio, slug, profile_image, etc.) to User model
- New PostUser M2M table (replaces post_authors for new posts)
- PostWriter service: direct DB CRUD with Lexical rendering, optimistic
  locking, AP federation, tag upsert
- Rewrite create/edit/settings routes to use PostWriter (no Ghost API calls)
- Neuter Ghost webhooks (post/page/author/tag → 204 no-op)
- Disable Ghost startup sync

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

shared/models/user.py

@@ -23,6 +23,17 @@ class User(Base):
     stripe_customer_id: Mapped[str | None] = mapped_column(String(255), index=True, nullable=True)
     ghost_raw: Mapped[dict | None] = mapped_column(JSONB, nullable=True)
 
+    # Author profile fields (merged from Ghost Author)
+    slug: Mapped[str | None] = mapped_column(String(191), unique=True, index=True, nullable=True)
+    bio: Mapped[str | None] = mapped_column(Text, nullable=True)
+    profile_image: Mapped[str | None] = mapped_column(Text, nullable=True)
+    cover_image: Mapped[str | None] = mapped_column(Text, nullable=True)
+    website: Mapped[str | None] = mapped_column(Text, nullable=True)
+    location: Mapped[str | None] = mapped_column(Text, nullable=True)
+    facebook: Mapped[str | None] = mapped_column(Text, nullable=True)
+    twitter: Mapped[str | None] = mapped_column(Text, nullable=True)
+    is_admin: Mapped[bool] = mapped_column(Boolean, nullable=False, default=False, server_default=func.false())
+
     # Relationships to Ghost-related entities
 
     user_newsletters = relationship("UserNewsletter", back_populates="user", cascade="all, delete-orphan", lazy="selectin")