fix(lidarr): send the artist add's monitor choice in addOptions (#5239)

ArtistResource has no top-level `monitor`. Lidarr reads the choice from
AddOptions (AddArtistOptions, a MonitoringOptions), so the "all"/"future"
we sent there was dropped on deserialisation. AddOptions.Monitor stayed
Unknown, and AlbumMonitoredService.SetAlbumMonitoredStatus returns early
on Unknown. The request's monitoring was never applied.

Send monitor and monitored inside addOptions with searchForMissingAlbums,
the shape Lidarr's getNewArtist.js posts, and set monitorNewItems "all"
explicitly: both choices mean new releases are watched.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

internal/lidarr/client.go

@@ -274,13 +274,20 @@ func (c *Client) LookupTrack(ctx context.Context, term string) ([]LookupResult,
 	return out, nil
 }
 
-// AddArtist posts to POST /api/v1/artist. MonitorAll=true sends monitor="all";
-// false sends "future". Returns nil on 2xx; typed error otherwise.
+// AddArtist posts to POST /api/v1/artist. MonitorAll=true monitors every
+// album ("all"); false monitors only releases from now on ("future"). New
+// releases are monitored either way. Returns nil on 2xx; typed error
+// otherwise.
 //
 // All four of artistName, foreignArtistId, qualityProfileId, and
 // metadataProfileId are required by Lidarr. Omitting any one produces a
 // 400 with field-level validation messages (e.g. "'Metadata Profile Id'
 // must be greater than '0'").
+//
+// The monitor choice belongs in addOptions (AddArtistOptions, a
+// MonitoringOptions). ArtistResource has no top-level `monitor`, so a
+// choice sent there is dropped, AddOptions.Monitor stays Unknown and
+// Lidarr skips applying it (#5239).
 func (c *Client) AddArtist(ctx context.Context, p AddArtistParams) error {
 	monitor := "future"
 	if p.MonitorAll {
@@ -293,8 +300,12 @@ func (c *Client) AddArtist(ctx context.Context, p AddArtistParams) error {
 		"metadataProfileId": p.MetadataProfileID,
 		"rootFolderPath":    p.RootFolderPath,
 		"monitored":         true,
-		"monitor":           monitor,
-		"addOptions":        map[string]any{"searchForMissingAlbums": true},
+		"monitorNewItems":   "all",
+		"addOptions": map[string]any{
+			"monitor":                monitor,
+			"monitored":              true,
+			"searchForMissingAlbums": true,
+		},
 	})
 	if err != nil {
 		return fmt.Errorf("%w: marshal: %v", ErrInvalidPayload, err)