feat(writers): quote default values based on SQL column type

Bun and GORM struct tags now emit quoted defaults for string/date/time/UUID
columns (e.g. default:'disconnected') and unquoted defaults for numeric and
boolean columns (e.g. default:0, default:true). Function-call expressions
such as now() or gen_random_uuid() are never quoted regardless of type.

Adds QuoteDefaultValue(value, sqlType) helper in pkg/writers and updates
both type mappers and the bun writer tests accordingly.

pkg/writers/writer.go

@@ -81,6 +81,64 @@ func SanitizeFilename(name string) string {
 	return name
 }
 
+// QuoteDefaultValue wraps a sanitized default value in single quotes when the SQL
+// column type requires it (strings, dates, times, UUIDs, enums). Numeric types
+// (integers, floats, serials) and boolean types are left unquoted. Function-call
+// expressions such as now() or gen_random_uuid() are always left unquoted regardless
+// of type, because they contain parentheses.
+//
+// Examples (varchar):   "disconnected" → "'disconnected'"
+// Examples (boolean):   "true"         → "true"
+// Examples (bigint):    "0"            → "0"
+// Examples (timestamp): "now()"        → "now()"   (function call – never quoted)
+func QuoteDefaultValue(value, sqlType string) string {
+	// Function calls are never quoted regardless of column type.
+	if strings.Contains(value, "(") || strings.Contains(value, ")") {
+		return value
+	}
+
+	// Normalise the SQL type: lowercase, strip length/precision suffix.
+	baseType := strings.ToLower(strings.TrimSpace(sqlType))
+	if idx := strings.Index(baseType, "("); idx > 0 {
+		baseType = baseType[:idx]
+	}
+
+	// Types whose default values must NOT be quoted.
+	unquotedTypes := map[string]bool{
+		// Integer types
+		"integer":     true,
+		"int":         true,
+		"int2":        true,
+		"int4":        true,
+		"int8":        true,
+		"smallint":    true,
+		"bigint":      true,
+		"serial":      true,
+		"smallserial": true,
+		"bigserial":   true,
+		// Float / numeric types
+		"real":             true,
+		"float":            true,
+		"float4":           true,
+		"float8":           true,
+		"double precision": true,
+		"numeric":          true,
+		"decimal":          true,
+		"money":            true,
+		// Boolean
+		"boolean": true,
+		"bool":    true,
+	}
+
+	if unquotedTypes[baseType] {
+		return value
+	}
+
+	// Everything else (text, varchar, char, uuid, date, time, timestamp, json, …)
+	// is treated as a quoted literal.
+	return "'" + value + "'"
+}
+
 // SanitizeStructTagValue sanitizes a value to be safely used inside Go struct tags.
 // Go struct tags are delimited by backticks, so any backtick in the value would break the syntax.
 // This function: