SOA as document: replace export with publish workflow

Statements of Applicability are no longer exported as one-off PDFs.
Instead, each SOA owns a persistent document that accumulates versions
over time, following the same publish/approve lifecycle as authored
documents.

Publishing without approvers publishes immediately; publishing with
approvers creates a draft pending approval via the existing quorum
system. SOAs can also store default approvers that are pre-populated in
the publish dialog.

The SOA is removed from the snapshot system — applicability statements
are now queried directly (snapshot_id IS NULL) rather than through
snapshot copies.

A standalone migration script (cmd/migrate-soa-snapshots-to-documents)
converts existing SOA snapshots into documents with proper ProseMirror
content, preserving version history and approval decisions.

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

pkg/cmd/soa/soa.go

@@ -20,6 +20,7 @@ import (
 	"go.probo.inc/probo/pkg/cmd/soa/create"
 	"go.probo.inc/probo/pkg/cmd/soa/delete"
 	"go.probo.inc/probo/pkg/cmd/soa/list"
+	"go.probo.inc/probo/pkg/cmd/soa/publish"
 	"go.probo.inc/probo/pkg/cmd/soa/statement"
 	"go.probo.inc/probo/pkg/cmd/soa/update"
 	"go.probo.inc/probo/pkg/cmd/soa/view"
@@ -36,6 +37,7 @@ func NewCmdSoa(f *cmdutil.Factory) *cobra.Command {
 	cmd.AddCommand(view.NewCmdView(f))
 	cmd.AddCommand(update.NewCmdUpdate(f))
 	cmd.AddCommand(delete.NewCmdDelete(f))
+	cmd.AddCommand(publish.NewCmdPublish(f))
 	cmd.AddCommand(statement.NewCmdStatement(f))
 
 	return cmd