feat(auth): store Subsonic API keys hashed; a new key is shown once (M462 #4983)

users.api_token held each user's apiKey in plaintext and was looked up by
equality, so a leaked row or backup handed out working keys. Migration
0063 replaces it with api_token_hash (sha256, hex), computed in place
from the existing keys so every Subsonic client keeps working.

The key can no longer be read back: GET /api/me/api-token is gone, and
POST returns the new key once. Settings shows it right after Regenerate
with a copy button and a "won't be shown again" note.

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

internal/subsonic/star_test.go

@@ -40,7 +40,7 @@ func testStarPool(t *testing.T) (*pgxpool.Pool, dbq.User, dbq.Track, dbq.Album,
 	dbtest.ResetDB(t, pool)
 	q := dbq.New(pool)
 	u, _ := q.CreateUser(context.Background(), dbq.CreateUserParams{
-		Username: dbtest.TestUserPrefix + "tester", PasswordHash: "x", ApiToken: "x", IsAdmin: false,
+		Username: dbtest.TestUserPrefix + "tester", PasswordHash: "x", ApiTokenHash: "x", IsAdmin: false,
 	})
 	a, _ := q.UpsertArtist(context.Background(), dbq.UpsertArtistParams{Name: "X", SortName: "X"})
 	al, _ := q.UpsertAlbum(context.Background(), dbq.UpsertAlbumParams{Title: "X", SortTitle: "X", ArtistID: a.ID})
@@ -228,7 +228,7 @@ func TestHandleGetStarred2_CrossUserIsolation(t *testing.T) {
 	pool, alice, track, _, _ := testStarPool(t)
 	q := dbq.New(pool)
 	bob, _ := q.CreateUser(context.Background(), dbq.CreateUserParams{
-		Username: dbtest.TestUserPrefix + "bob", PasswordHash: "x", ApiToken: "y", IsAdmin: false,
+		Username: dbtest.TestUserPrefix + "bob", PasswordHash: "x", ApiTokenHash: "y", IsAdmin: false,
 	})
 	_, _ = q.LikeTrack(context.Background(), dbq.LikeTrackParams{UserID: alice.ID, TrackID: track.ID})