fix(dbml): resolve commented cross-file // Ref: lines

Commented refs are collected per file and resolved against the combined
model after all inputs are loaded (directory, --from-list, merge, jobs).
Matched refs become FKs and relationships; duplicates of existing FKs are
skipped; missing targets are skipped with a warning; column type
mismatches warn.

Also keep reused index names within a DBML table instead of overwriting,
give a second FK to the same table a distinct relationship name, and make
the pgsql writer match relationships to FKs by name first.

cmd/relspec/job.go

@@ -578,6 +578,7 @@ func runMergeJob(rj *resolvedJob, lg *jobLogger) error {
 		lg.logf("merging: %s", inputLabel(ri))
 		merge.MergeDatabases(base, db, opts)
 	}
+	finalizeCommentedRefs(base, func(w string) { lg.logf("warning: %s", w) })
 	base.UpdateDate()
 	return writeJobOutput(rj, base, lg)
 }
@@ -814,6 +815,7 @@ func readJobInputs(rj *resolvedJob, lg *jobLogger) (*models.Database, error) {
 	if base == nil {
 		return nil, fmt.Errorf("no inputs produced a database")
 	}
+	finalizeCommentedRefs(base, func(w string) { lg.logf("warning: %s", w) })
 	return base, nil
 }