feat(migration): add fallback for column type conversion failures

* implement renaming of old column and adding new column on conversion failure
* update templates and tests to support new behavior

pkg/writers/pgsql/writer_test.go

@@ -1106,6 +1106,42 @@ func TestWriteSchema_EmitsGuardedAlterColumnTypeStatements(t *testing.T) {
 	}
 }
 
+func TestWriteSchema_GuardedAlterColumnTypeFallsBackOnConversionFailure(t *testing.T) {
+	db := models.InitDatabase("testdb")
+	schema := models.InitSchema("public")
+
+	table := models.InitTable("agent_skills", "public")
+
+	nameCol := models.InitColumn("name", "agent_skills", "public")
+	nameCol.Type = "integer"
+	table.Columns["name"] = nameCol
+
+	schema.Tables = append(schema.Tables, table)
+	db.Schemas = append(db.Schemas, schema)
+
+	var buf bytes.Buffer
+	writer := NewWriter(&writers.WriterOptions{})
+	writer.writer = &buf
+
+	if err := writer.WriteDatabase(db); err != nil {
+		t.Fatalf("WriteDatabase failed: %v", err)
+	}
+
+	output := buf.String()
+	if !strings.Contains(output, "EXCEPTION WHEN OTHERS THEN") {
+		t.Fatalf("expected guarded alter to fall back on conversion failure, got:\n%s", output)
+	}
+	if !strings.Contains(output, "renamed_column := 'name_' || trim(both '_' from regexp_replace(lower(current_type)") {
+		t.Fatalf("expected fallback to derive a renamed column name from the live type, got:\n%s", output)
+	}
+	if !strings.Contains(output, "RENAME COLUMN name TO %I") {
+		t.Fatalf("expected fallback to rename the existing column, got:\n%s", output)
+	}
+	if !strings.Contains(output, "ADD COLUMN name integer") {
+		t.Fatalf("expected fallback to add a fresh column with the new type, got:\n%s", output)
+	}
+}
+
 func TestWriteSchema_UsesStorageTypeForSerialAlterStatements(t *testing.T) {
 	db := models.InitDatabase("testdb")
 	schema := models.InitSchema("public")