feat: COM-port support for workstation devices + agent UI fixes

- EquipmentPage: add COM-port connection type with port field (COM1, /dev/ttyUSB0)
- api.ts: add comPort field to WorkstationDevice type
- workstations route: pass com_port to INSERT/PATCH
- migration 042: extend connection check constraint to include 'com', add com_port column
- agent index.html: highlight first cell on load, reset input on unpair

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

backend/migrations/042_workstation_devices_com.sql

@@ -0,0 +1,13 @@
+-- Добавляем поддержку COM-порта для устройств рабочего места
+
+-- Расширяем CHECK constraint для connection (добавляем 'com')
+ALTER TABLE workstation_devices
+  DROP CONSTRAINT IF EXISTS workstation_devices_connection_check;
+
+ALTER TABLE workstation_devices
+  ADD CONSTRAINT workstation_devices_connection_check
+    CHECK (connection IN ('usb', 'network', 'com'));
+
+-- Добавляем поле com_port (например: COM1, COM3, /dev/ttyUSB0)
+ALTER TABLE workstation_devices
+  ADD COLUMN IF NOT EXISTS com_port VARCHAR(50);