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.

pkg/writers/pgsql/writer.go

@@ -1259,13 +1259,18 @@ func (w *Writer) writeForeignKeys(schema *models.Schema) error {
 				fkName = fmt.Sprintf("fk_%s_%s", table.SQLName(), rel.ToTable)
 			}
 
-			// Find the foreign key constraint that matches this relationship
+			// Find the foreign key constraint that matches this relationship.
+			// Prefer the exact name: with several FKs to the same table, a
+			// referenced-table match alone picks an arbitrary one.
 			var fkConstraint *models.Constraint
-			for _, constraint := range table.Constraints {
-				if constraint.Type == models.ForeignKeyConstraint &&
-					(constraint.Name == fkName || constraint.ReferencedTable == rel.ToTable) {
-					fkConstraint = constraint
-					break
+			if c, ok := table.Constraints[fkName]; ok && c.Type == models.ForeignKeyConstraint {
+				fkConstraint = c
+			} else {
+				for _, constraint := range sortConstraints(table.Constraints) {
+					if constraint.Type == models.ForeignKeyConstraint && constraint.ReferencedTable == rel.ToTable {
+						fkConstraint = constraint
+						break
+					}
 				}
 			}