feat(series): SeriesPage model + 0005 migration (unique image, ordered pages)

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

backend/app/models/__init__.py

@@ -11,6 +11,7 @@ from .import_settings import ImportSettings
 from .import_task import ImportTask
 from .ml_settings import MLSettings
 from .post import Post
+from .series_page import SeriesPage
 from .source import Source
 from .tag import Tag, TagKind, image_tag
 from .tag_alias import TagAlias
@@ -24,6 +25,7 @@ __all__ = [
     "Source",
     "Credential",
     "Post",
+    "SeriesPage",
     "ImageRecord",
     "ImageProvenance",
     "Tag",

backend/app/models/series_page.py

@@ -0,0 +1,38 @@
+"""SeriesPage — ordered image membership for a series-kind Tag.
+
+A series IS a Tag with kind='series'; series_page gives it ordered pages.
+An image belongs to at most one series (UNIQUE image_id). Cover = the
+lowest page_number. page_number is an ordering key only (not unique) —
+reorder rewrites 1..N wholesale.
+"""
+
+from datetime import datetime
+
+from sqlalchemy import DateTime, ForeignKey, Integer, func
+from sqlalchemy.orm import Mapped, mapped_column
+
+from .base import Base
+
+
+class SeriesPage(Base):
+    __tablename__ = "series_page"
+
+    id: Mapped[int] = mapped_column(Integer, primary_key=True)
+    series_tag_id: Mapped[int] = mapped_column(
+        ForeignKey("tag.id", ondelete="CASCADE"), nullable=False, index=True
+    )
+    image_id: Mapped[int] = mapped_column(
+        ForeignKey("image_record.id", ondelete="CASCADE"),
+        nullable=False,
+        unique=True,
+    )
+    page_number: Mapped[int] = mapped_column(Integer, nullable=False)
+    created_at: Mapped[datetime] = mapped_column(
+        DateTime(timezone=True), nullable=False, server_default=func.now()
+    )
+    updated_at: Mapped[datetime] = mapped_column(
+        DateTime(timezone=True),
+        nullable=False,
+        server_default=func.now(),
+        onupdate=func.now(),
+    )