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>

account/alembic/versions/0003_add_user_profile_fields.py

@@ -0,0 +1,43 @@
+"""Add author profile fields to users table.
+
+Merges Ghost Author profile data into User — bio, profile_image, cover_image,
+website, location, facebook, twitter, slug, is_admin.
+
+Revision ID: 0003
+Revises: 0002_hash_oauth_tokens
+"""
+from alembic import op
+import sqlalchemy as sa
+
+revision = "0003"
+down_revision = "0002_hash_oauth_tokens"
+branch_labels = None
+depends_on = None
+
+
+def upgrade():
+    op.add_column("users", sa.Column("slug", sa.String(191), nullable=True))
+    op.add_column("users", sa.Column("bio", sa.Text(), nullable=True))
+    op.add_column("users", sa.Column("profile_image", sa.Text(), nullable=True))
+    op.add_column("users", sa.Column("cover_image", sa.Text(), nullable=True))
+    op.add_column("users", sa.Column("website", sa.Text(), nullable=True))
+    op.add_column("users", sa.Column("location", sa.Text(), nullable=True))
+    op.add_column("users", sa.Column("facebook", sa.Text(), nullable=True))
+    op.add_column("users", sa.Column("twitter", sa.Text(), nullable=True))
+    op.add_column("users", sa.Column(
+        "is_admin", sa.Boolean(), nullable=False, server_default=sa.text("false"),
+    ))
+    op.create_index("ix_users_slug", "users", ["slug"], unique=True)
+
+
+def downgrade():
+    op.drop_index("ix_users_slug")
+    op.drop_column("users", "is_admin")
+    op.drop_column("users", "twitter")
+    op.drop_column("users", "facebook")
+    op.drop_column("users", "location")
+    op.drop_column("users", "website")
+    op.drop_column("users", "cover_image")
+    op.drop_column("users", "profile_image")
+    op.drop_column("users", "bio")
+    op.drop_column("users", "slug")