feat(config): add recommendation section (weighted shuffle weights)

BaseWeight, LikeBoost, RecencyWeight, SkipPenalty, JitterMagnitude,
RecentlyPlayedHours, RadioSize, RadioSizeMax. Defaults match spec §6.

internal/config/config.go

@@ -10,13 +10,14 @@ import (
 )
 
 type Config struct {
-	Server   ServerConfig   `yaml:"server"`
-	Database DatabaseConfig `yaml:"database"`
-	Log      LogConfig      `yaml:"log"`
-	Auth     AuthConfig     `yaml:"auth"`
-	Library  LibraryConfig  `yaml:"library"`
-	Subsonic SubsonicConfig `yaml:"subsonic"`
-	Events   EventsConfig   `yaml:"events"`
+	Server         ServerConfig         `yaml:"server"`
+	Database       DatabaseConfig       `yaml:"database"`
+	Log            LogConfig            `yaml:"log"`
+	Auth           AuthConfig           `yaml:"auth"`
+	Library        LibraryConfig        `yaml:"library"`
+	Subsonic       SubsonicConfig       `yaml:"subsonic"`
+	Events         EventsConfig         `yaml:"events"`
+	Recommendation RecommendationConfig `yaml:"recommendation"`
 }
 
 type ServerConfig struct {
@@ -63,6 +64,19 @@ type EventsConfig struct {
 	SkipMaxDurationPlayedMs int     `yaml:"skip_max_duration_played_ms"`
 }
 
+// RecommendationConfig governs the M3 weighted-shuffle scoring (spec §6).
+// All weights are operator-tunable; defaults match the spec recommendations.
+type RecommendationConfig struct {
+	BaseWeight          float64 `yaml:"base_weight"`
+	LikeBoost           float64 `yaml:"like_boost"`
+	RecencyWeight       float64 `yaml:"recency_weight"`
+	SkipPenalty         float64 `yaml:"skip_penalty"`
+	JitterMagnitude     float64 `yaml:"jitter_magnitude"`
+	RecentlyPlayedHours int     `yaml:"recently_played_hours"`
+	RadioSize           int     `yaml:"radio_size"`
+	RadioSizeMax        int     `yaml:"radio_size_max"`
+}
+
 func Default() Config {
 	return Config{
 		Server:   ServerConfig{Address: ":4533"},
@@ -73,6 +87,16 @@ func Default() Config {
 			SkipMaxCompletionRatio:  0.5,
 			SkipMaxDurationPlayedMs: 30000,
 		},
+		Recommendation: RecommendationConfig{
+			BaseWeight:          1.0,
+			LikeBoost:           2.0,
+			RecencyWeight:       1.0,
+			SkipPenalty:         1.0,
+			JitterMagnitude:     0.1,
+			RecentlyPlayedHours: 1,
+			RadioSize:           50,
+			RadioSizeMax:        200,
+		},
 	}
 }