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Drops the unused tag.namespace column from FC-1 — superseded by kind.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

@@ -6,9 +6,12 @@ from .credential import Credential
 from .download_event import DownloadEvent
 from .image_provenance import ImageProvenance
 from .image_record import ImageRecord
+from .import_batch import ImportBatch
+from .import_settings import ImportSettings
+from .import_task import ImportTask
 from .post import Post
 from .source import Source
-from .tag import Tag, image_tag
+from .tag import Tag, TagKind, image_tag
 
 __all__ = [
     "Base",
@@ -19,6 +22,10 @@ __all__ = [
     "ImageRecord",
     "ImageProvenance",
     "Tag",
+    "TagKind",
     "image_tag",
     "DownloadEvent",
+    "ImportBatch",
+    "ImportTask",
+    "ImportSettings",
 ]