feat(07-02): implement PrintConfig function with comment annotations
- Add AutoClasses map[TrafficClass]bool to LoadResult for tracking auto-assigned classes
- PrintConfig() returns commented TOML with header (source, date), [[rules]] section, [sounds.*] section
- waveformString() helper converts WaveformType back to string
- classAnnotation() returns default/override/auto-assigned per class
- Built-in classes emitted in AllClasses() order; user-defined classes sorted alphabetically
- Rules section emits [[rules]] blocks; port omitted when DstPort==0
- Tests: TestPrintConfigContainsAllClasses, TestPrintConfigSourcePath, TestPrintConfigNoSourcePath,
TestPrintConfigContainsRules, TestPrintConfigRuleNoPort, TestPrintConfigDefaultAnnotation,
TestPrintConfigOverrideAnnotation, TestPrintConfigAutoAssignedAnnotation