feat(tournament): implement class merging and pool management features

- Added mergeClassesIntoPool and resetPool functions in tournamentService to handle merging classes into a common pool and resetting pool assignments.
- Introduced new API routes for merging and resetting pools in tournamentRoutes.
- Enhanced TournamentGroupsTab component with UI for merging classes, including selection for source and target classes, strategy options, and out-of-competition settings.
- Updated localization files to include new strings related to class merging functionality.
- Modified TournamentTab to handle merge pool events and manage API interactions for merging classes.

backend/migrations/20260107_add_pool_and_out_of_competition.sql

@@ -0,0 +1,11 @@
+-- Add pool_id to tournament_group for pooled group phases
+ALTER TABLE `tournament_group`
+  ADD COLUMN `pool_id` INT NULL AFTER `class_id`;
+
+-- Add out_of_competition flags
+ALTER TABLE `tournament_member`
+  ADD COLUMN `out_of_competition` TINYINT(1) NOT NULL DEFAULT 0 AFTER `class_id`;
+
+ALTER TABLE `external_tournament_participant`
+  ADD COLUMN `out_of_competition` TINYINT(1) NOT NULL DEFAULT 0 AFTER `class_id`;
+