feat(gyms): gym logo field; other-gym navbar button uses that gym's brand colour and logo

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

database/migration_20261013_gym_brand_color.sql

@@ -3,3 +3,6 @@
 -- Safe to re-run.
 ALTER TABLE `gyms` ADD COLUMN IF NOT EXISTS `brand_color` VARCHAR(7) NOT NULL DEFAULT '' AFTER `has_crossfit`;
 UPDATE `gyms` SET `brand_color` = '#C2D500' WHERE `id` = 1 AND `brand_color` = '';
+
+-- Logótipo do ginásio (caminho relativo, ex.: site/assets/img/logos/ginasio.svg).
+ALTER TABLE `gyms` ADD COLUMN IF NOT EXISTS `logo` VARCHAR(255) NOT NULL DEFAULT '' AFTER `brand_color`;