feat: generated and identity columns for mssql, sqlite, drizzle, typeorm, bun and gorm readers

- mssql: write computed columns (AS (expr) PERSISTED) and identity; read computed definition and identity
- sqlite: write GENERATED ALWAYS AS (expr) STORED; read generated columns via table_xinfo and parse the expression
- drizzle: generatedAlwaysAs / generated(Always|ByDefault)AsIdentity, read and write
- typeorm: asExpression/generatedType and identity decorators, read and write; decorator scan is now quote-aware
- bun, gorm readers: read generated and identity markers
- readmes updated

pkg/writers/sqlite/writer_test.go

@@ -421,3 +421,39 @@ func TestQuoteIdentifier(t *testing.T) {
 		}
 	}
 }
+
+func TestWriteDatabase_GeneratedColumn(t *testing.T) {
+	table := models.InitTable("people", "public")
+	first := models.InitColumn("first", "people", "public")
+	first.Type = "text"
+	first.Sequence = 1
+	table.Columns["first"] = first
+	full := models.InitColumn("full_name", "people", "public")
+	full.Type = "text"
+	full.Sequence = 2
+	full.NotNull = true
+	full.Generated = true
+	full.GenerationExpression = "first || ' ' || first"
+	full.Default = "ignored"
+	table.Columns["full_name"] = full
+
+	schema := models.InitSchema("public")
+	schema.Tables = append(schema.Tables, table)
+	db := models.InitDatabase("testdb")
+	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)
+	}
+
+	want := `"full_name" TEXT GENERATED ALWAYS AS (first || ' ' || first) STORED NOT NULL`
+	if !strings.Contains(buf.String(), want) {
+		t.Errorf("missing %q in:\n%s", want, buf.String())
+	}
+	if strings.Contains(buf.String(), "DEFAULT") && strings.Contains(buf.String(), "ignored") {
+		t.Errorf("generated column must not carry a DEFAULT:\n%s", buf.String())
+	}
+}