feat(fc2a): schema migration 0002 — tag kinds + fandom hierarchy + import lifecycle

Adds Tag.kind enum (artist/character/fandom/general/series/archive/post/meta/rating),
Tag.fandom_id FK with CHECK constraint (only valid for kind='character'), and a
kind-aware uniqueness index so the same name can exist across kinds and the same
character name can exist in different fandoms.

Adds ImportBatch + ImportTask state-machine tables for scan tracking, plus a
single-row ImportSettings table (CHECK id=1) holding the importer's filter knobs.

Adds image_record.integrity_status column (defaults to 'unknown'); FC-2e
populates this via the integrity verifier.

Drops the unused tag.namespace column from FC-1 — superseded by kind.

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

backend/app/models/import_batch.py

@@ -0,0 +1,32 @@
+"""ImportBatch — one scan run, aggregating many ImportTasks."""
+
+from datetime import datetime
+
+from sqlalchemy import DateTime, Integer, String, Text, func
+from sqlalchemy.orm import Mapped, mapped_column, relationship
+
+from .base import Base
+
+
+class ImportBatch(Base):
+    __tablename__ = "import_batch"
+
+    id: Mapped[int] = mapped_column(Integer, primary_key=True)
+    triggered_by: Mapped[str] = mapped_column(String(32), nullable=False)
+    source_path: Mapped[str] = mapped_column(Text, nullable=False)
+    scan_mode: Mapped[str] = mapped_column(String(16), nullable=False)  # quick|deep
+
+    started_at: Mapped[datetime] = mapped_column(
+        DateTime(timezone=True), nullable=False, server_default=func.now()
+    )
+    finished_at: Mapped[datetime | None] = mapped_column(DateTime(timezone=True), nullable=True)
+
+    total_files: Mapped[int] = mapped_column(Integer, nullable=False, default=0)
+    imported: Mapped[int] = mapped_column(Integer, nullable=False, default=0)
+    skipped: Mapped[int] = mapped_column(Integer, nullable=False, default=0)
+    failed: Mapped[int] = mapped_column(Integer, nullable=False, default=0)
+
+    status: Mapped[str] = mapped_column(String(16), nullable=False, default="running", index=True)
+    # running | complete | cancelled
+
+    tasks = relationship("ImportTask", back_populates="batch", cascade="all, delete-orphan")