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>

src/lib/api.ts

@@ -972,9 +972,10 @@ export interface WorkstationDevice {
   workstationId: string
   type: 'kkt' | 'printer'
   name: string
-  connection: 'usb' | 'network'
+  connection: 'usb' | 'network' | 'com'
   networkHost?: string
   networkPort?: number
+  comPort?: string
   purpose: 'fiscal' | 'kitchen' | 'bar' | 'receipt' | 'other'
   config: Record<string, unknown>
 }