chore: mark *.pb.go as generated in .gitattributes

Collapses protobuf bindings in PR diffs and excludes them from
linguist language stats.

Assisted-by: Claude Code
Signed-off-by: Jose I. Paris <jiparis@chainloop.dev>

Chainloop-Trace-Sessions: 234a03ed-b238-4506-95f0-235242842db2
Signed-off-by: Jose I. Paris <jiparis@chainloop.dev>

Author: jiparis

.gitattributes

@@ -4,4 +4,7 @@ app/controlplane/pkg/data/ent/migrate/** linguist-generated=false
 app/controlplane/pkg/data/ent/migrate/** linguist-detectable=true
 app/controlplane/pkg/data/ent/schema/* linguist-generated=false
 app/controlplane/pkg/data/ent/schema/* linguist-detectable=true
-app/controlplane/api/gen/jsonschema/** linguist-generated=true
+app/controlplane/api/gen/jsonschema/** linguist-generated=true
+*.pb.go linguist-generated=true
+*.pb.validate.go linguist-generated=true
+wire_gen.go linguist-generated=true