fix: Add migration SQL files to repository

migrations/003_create_realtime_events.sql

@@ -0,0 +1,19 @@
+-- Migration: Create realtime_events table
+-- Description: Ring buffer untuk realtime stream & SSE events
+-- Date: 2024-12-28
+
+CREATE TABLE IF NOT EXISTS realtime_events (
+    id BIGINT UNSIGNED AUTO_INCREMENT PRIMARY KEY,
+    created_at DATETIME NOT NULL DEFAULT CURRENT_TIMESTAMP,
+    location_code VARCHAR(64) NOT NULL,
+    gate_code VARCHAR(64) NOT NULL,
+    category VARCHAR(64) NOT NULL,
+    event_time INT UNSIGNED NOT NULL COMMENT 'Unix timestamp',
+    total_count_delta INT NOT NULL DEFAULT 1 COMMENT 'Delta count untuk event ini (biasanya 1)',
+    INDEX idx_created_at (created_at),
+    INDEX idx_location_gate (location_code, gate_code)
+) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_unicode_ci;
+
+-- Optional: Cleanup old events (older than 7 days) via cron or manual
+-- DELETE FROM realtime_events WHERE created_at < DATE_SUB(NOW(), INTERVAL 7 DAY);
+