Scope sub-third-parties per parent

Replace the many-to-many junction table with a direct
parent_third_party_id foreign key on third_parties. Each
sub-third-party now belongs to exactly one parent, making
duplicates across parents independent entities.

Replace the firstLevel boolean with an integer level field
(1 = direct, 2+ = parent level + 1) to support arbitrary
nesting depth.

Remove the createThirdPartyThirdPartyMapping and
deleteThirdPartyThirdPartyMapping mutations, the CLI
link/unlink commands, and the corresponding MCP tools.
Creating a child third party now just requires passing
parentThirdPartyId on the existing createThirdParty mutation.

The frontend walks the parentThirdParty chain to build
display names like "Name (Ancestor1/Ancestor2)" and shows
clickable ancestor links on the detail page.

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

pkg/cookiebanner/tracker_mapping_worker.go

@@ -1141,8 +1141,16 @@ func (h *trackerMappingHandler) prepareOrgThirdParty(
 		return prep, fmt.Errorf("cannot load common third party domains: %w", err)
 	}
 
+	firstLevel := 1
+
 	var orgThirdParties coredata.ThirdParties
-	if err := orgThirdParties.LoadAllByOrganizationID(ctx, conn, scope, tp.OrganizationID); err != nil {
+	if err := orgThirdParties.LoadAllByOrganizationID(
+		ctx,
+		conn,
+		scope,
+		tp.OrganizationID,
+		coredata.NewThirdPartyFilter(nil, &firstLevel, nil),
+	); err != nil {
 		return prep, fmt.Errorf("cannot load org third parties: %w", err)
 	}