feat: Implement campaign synchronization feature with dropdown UI

- Updated SCSS styles for new campaign sync buttons and dropdowns.
- Refactored main_view.php to replace the single select for campaigns with a multi-select dropdown.
- Added JavaScript functions to handle dropdown interactions and sync status updates.
- Introduced sync status bars for clients in main_view.php.
- Created new database migrations for client sync flags and cron sync status tracking.

migrations/012_cron_sync_status.sql

@@ -0,0 +1,57 @@
+-- Migracja: tabela cron_sync_status zamiast JSON w settings
+-- Data: 2026-02-19
+-- Opis: dedykowana tabela do sledzenia postepu pipeline CRON (kampanie, produkty)
+
+CREATE TABLE IF NOT EXISTS `cron_sync_status` (
+  `id` INT AUTO_INCREMENT PRIMARY KEY,
+  `client_id` INT NOT NULL,
+  `pipeline` ENUM('campaigns','products') NOT NULL,
+  `sync_date` DATE NOT NULL,
+  `phase` ENUM('pending','fetch','aggregate_30','aggregate_temp','done') NOT NULL DEFAULT 'pending',
+  `started_at` DATETIME NULL,
+  `completed_at` DATETIME NULL,
+  `error_message` TEXT NULL,
+  `created_at` DATETIME NOT NULL DEFAULT CURRENT_TIMESTAMP,
+  UNIQUE KEY `uq_client_pipeline_date` (`client_id`, `pipeline`, `sync_date`),
+  KEY `idx_pipeline_phase` (`pipeline`, `phase`),
+  KEY `idx_client_id` (`client_id`)
+) ENGINE=InnoDB DEFAULT CHARSET=utf8;
+
+-- Usuniecie kolumny force_sync_campaigns z clients
+SET @sql = IF(
+  EXISTS (
+    SELECT 1
+    FROM INFORMATION_SCHEMA.COLUMNS
+    WHERE TABLE_SCHEMA = DATABASE()
+      AND TABLE_NAME = 'clients'
+      AND COLUMN_NAME = 'force_sync_campaigns'
+  ),
+  'ALTER TABLE `clients` DROP COLUMN `force_sync_campaigns`',
+  'DO 1'
+);
+PREPARE stmt FROM @sql;
+EXECUTE stmt;
+DEALLOCATE PREPARE stmt;
+
+-- Usuniecie kolumny force_sync_products z clients
+SET @sql = IF(
+  EXISTS (
+    SELECT 1
+    FROM INFORMATION_SCHEMA.COLUMNS
+    WHERE TABLE_SCHEMA = DATABASE()
+      AND TABLE_NAME = 'clients'
+      AND COLUMN_NAME = 'force_sync_products'
+  ),
+  'ALTER TABLE `clients` DROP COLUMN `force_sync_products`',
+  'DO 1'
+);
+PREPARE stmt FROM @sql;
+EXECUTE stmt;
+DEALLOCATE PREPARE stmt;
+
+-- Usuniecie starych kluczy JSON z settings
+DELETE FROM `settings` WHERE `setting_key` IN (
+  'cron_campaigns_window_state',
+  'cron_campaigns_state',
+  'cron_products_pipeline_state'
+);