feat(backend): per-file review status with DSL filter and bulk endpoint

Replaces the old "untagged" sentinel tag with a proper per-file workflow
status: needs_review starts true on upload/import and is cleared by an
explicit action (no auto-clear on tagging). Surfaced as a filter token
(r=1 needs review, r=0 done) so it combines with tag/MIME conditions, and
toggled via POST /files/bulk/review (single id or many, edit-ACL enforced,
audit-logged as file_review).

needs_review lives on data.files (column added to the original 003 migration,
partial index in 006, action type seeded in 007).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

backend/internal/port/repository.go

@@ -48,6 +48,8 @@ type FileRepo interface {
 	Create(ctx context.Context, f *domain.File) (*domain.File, error)
 	// Update applies partial metadata changes and returns the updated record.
 	Update(ctx context.Context, id uuid.UUID, f *domain.File) (*domain.File, error)
+	// SetNeedsReview sets the review status on the given (non-trashed) files.
+	SetNeedsReview(ctx context.Context, ids []uuid.UUID, value bool) error
 	// SoftDelete moves a file to trash (sets is_deleted = true).
 	SoftDelete(ctx context.Context, id uuid.UUID) error
 	// Restore moves a file out of trash (sets is_deleted = false).