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/recommendation/suggestions_integration_test.go

@@ -42,7 +42,7 @@ func seedUser(t *testing.T, pool *pgxpool.Pool, name string) dbq.User {
 	t.Helper()
 	u, err := dbq.New(pool).CreateUser(context.Background(), dbq.CreateUserParams{
 		Username: dbtest.TestUserPrefix + name, PasswordHash: "x",
-		ApiToken: name + "-token", IsAdmin: false,
+		ApiTokenHash: name + "-token", IsAdmin: false,
 	})
 	if err != nil {
 		t.Fatalf("seed user: %v", err)