feat(07-01): add RawRule, LoadResult, validation, auto-freq to config package

- Add RawRule struct with Port *uint16, Protocol, Class fields
- Add LoadResult struct with FreqCfgs, UserRules, ConfigPath fields
- Change Load() signature to return LoadResult instead of bare map
- Add validateRules: checks protocol required, class required, valid protocols
- Add convertRules: converts RawRule slices to classify.Rule slices
- Add autoAssignFreq: FNV-32a deterministic Hz in [1200-2350] range
- Add addAutoFreqEntries: creates FreqConfig for new class names, skips built-ins
- Reorder ops: addAutoFreqEntries before merge so sounds overrides apply to user classes
- Update main.go call site to use LoadResult.FreqCfgs
- Update all 8 existing tests to use LoadResult return type
- Add 13 new tests covering rule parsing, validation, auto-freq, and LoadResult

cmd/netsynth/main.go

@@ -84,10 +84,11 @@ func run(cmd *cobra.Command, args []string) error {
 	}
 
 	// Load config (CFG-01 through CFG-05, D-11: fail fast before capture)
-	freqCfgs, err := config.Load(configPath)
+	loadResult, err := config.Load(configPath)
 	if err != nil {
 		return err
 	}
+	freqCfgs := loadResult.FreqCfgs
 
 	// Resolve output path
 	if outputPath == "" {