Drop legacy document columns and approver tables

The title, classification, and document_type columns have been moved to
document_versions. The document_approvers and document_version_approvers
tables have been replaced by approval quorums and decisions.

Signed-off-by: Sacha Al Himdani <sacha@getprobo.com>

pkg/coredata/migrations/20260328T120000Z.sql

@@ -1,2 +1 @@
--- TODO: drop the classification column from documents.
 ALTER TABLE documents ALTER COLUMN classification SET DEFAULT 'SECRET';