feat(pgsql): diff against the live database by default for direct output

Direct pgsql output (job output.conn_env, merge --output-conn) now reads the live
schema and executes only the differences. full_ddl: true (job option) or --full-ddl
(merge) restores the full idempotent DDL; file output is unchanged.

- compare PKs by columns, skip constraint-backed indexes, normalize index method,
  FK actions, serial/numeric types, default literals/casts and truncated names
- diff table and column comments instead of re-emitting them
- remove leftover ZZDUMP debug code

cmd/relspec/job.go

@@ -844,7 +844,7 @@ func writeJobOutput(rj *resolvedJob, db *models.Database, lg *jobLogger) error {
 		}
 		lg.logf("writing output to database env:%s", rj.outputConnEnv)
 		writerOpts := newWriterOptions("", o.Package, o.FlattenSchema, o.Types, o.ArrayNullable, o.ContinueOnError)
-		writerOpts.Metadata = map[string]interface{}{"connection_string": rj.outputConn}
+		writerOpts.Metadata = map[string]interface{}{"connection_string": rj.outputConn, "full_ddl": o.FullDDL}
 		return wpgsql.NewWriter(writerOpts).WriteDatabase(db)
 	}