Session 3: Radarr/Sonarr/Lidarr clients with add-on-search

Adds internal/arr with a shared HTTP layer and per-service clients that
look up candidates and POST the chosen one back with monitored=true and
search-on-add enabled. Lidarr requires metadata_profile_id, now part of
ArrConfig and validated when lidarr is set.

internal/config/config.go

@@ -40,6 +40,8 @@ type ArrConfig struct {
 	APIKey           string `yaml:"api_key"`
 	QualityProfileID int    `yaml:"quality_profile_id"`
 	RootFolder       string `yaml:"root_folder"`
+	// MetadataProfileID is required by Lidarr; ignored by Radarr/Sonarr.
+	MetadataProfileID int `yaml:"metadata_profile_id"`
 }
 
 func Load(path string) (*Config, error) {
@@ -108,6 +110,9 @@ func (c *Config) validate() error {
 			return fmt.Errorf("services.%s.quality_profile_id is required when service is set", name)
 		}
 	}
+	if c.Services.Lidarr != nil && c.Services.Lidarr.MetadataProfileID == 0 {
+		return fmt.Errorf("services.lidarr.metadata_profile_id is required when lidarr is set")
+	}
 	return nil
 }