feat(server): expose main credit stat to reflect only album artist | artist credit (#4268)

* attempt using artist | albumartist

* add primary stats, expose to ND and Subsonic

* response to feedback (1)

* address feedback part 1

* fix docs and artist show

* fix migration order

---------

Co-authored-by: Deluan Quintão <deluan@navidrome.org>

db/migrations/20250701010106_add_participant_stats_to_all_artists.sql

@@ -0,0 +1,65 @@
+-- +goose Up
+-- +goose StatementBegin
+WITH artist_role_counters AS (
+    SELECT jt.atom AS artist_id,
+            substr(
+                    replace(jt.path, '$.', ''),
+                    1,
+                    CASE WHEN instr(replace(jt.path, '$.', ''), '[') > 0
+                            THEN instr(replace(jt.path, '$.', ''), '[') - 1
+                        ELSE length(replace(jt.path, '$.', ''))
+                        END
+            ) AS role,
+            count(DISTINCT mf.album_id) AS album_count,
+            count(mf.id) AS count,
+            sum(mf.size) AS size
+    FROM media_file mf
+    JOIN json_tree(mf.participants) jt ON jt.key = 'id' AND jt.atom IS NOT NULL
+    GROUP BY jt.atom, role
+),
+artist_total_counters AS (
+    SELECT mfa.artist_id,
+            'total' AS role,
+            count(DISTINCT mf.album_id) AS album_count,
+            count(DISTINCT mf.id) AS count,
+            sum(mf.size) AS size
+    FROM media_file_artists mfa
+    JOIN media_file mf ON mfa.media_file_id = mf.id
+    GROUP BY mfa.artist_id
+),
+artist_participant_counter AS (
+    SELECT mfa.artist_id,
+        'maincredit' AS role,
+        count(DISTINCT mf.album_id) AS album_count,
+        count(DISTINCT mf.id) AS count,
+        sum(mf.size) AS size
+    FROM media_file_artists mfa
+    JOIN media_file mf ON mfa.media_file_id = mf.id
+    AND mfa.role IN ('albumartist', 'artist')
+    GROUP BY mfa.artist_id
+),
+combined_counters AS (
+    SELECT artist_id, role, album_count, count, size FROM artist_role_counters
+    UNION
+    SELECT artist_id, role, album_count, count, size FROM artist_total_counters
+    UNION
+    SELECT artist_id, role, album_count, count, size FROM artist_participant_counter
+),
+artist_counters AS (
+    SELECT artist_id AS id,
+            json_group_object(
+                    replace(role, '"', ''),
+                    json_object('a', album_count, 'm', count, 's', size)
+            ) AS counters
+    FROM combined_counters
+    GROUP BY artist_id
+)
+UPDATE artist
+SET stats = coalesce((SELECT counters FROM artist_counters ac WHERE ac.id = artist.id), '{}'),
+    updated_at = datetime(current_timestamp, 'localtime')
+WHERE artist.id <> '';
+-- +goose StatementEnd
+
+-- +goose Down
+-- +goose StatementBegin
+-- +goose StatementEnd