feat: printer duplicate copies setting (Feature 1)

- Add `duplicates` column (0-9) to printers table via migration
- Print loop repeats job 1+duplicates times per printer zone
- PrinterForm in Settings > Print now has ΑΝΤΙΓΡΑΦΑ (0-9) field
- PrinterRow shows amber badge when duplicates > 0

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

local_backend/schemas/printer.py

@@ -12,6 +12,7 @@ class PrinterBase(BaseModel):
     is_active: bool = True
     protocol: str = "escpos_tcp"
     line_width: int = 48
+    duplicates: int = 0
 
 
 class PrinterCreate(PrinterBase):
@@ -25,6 +26,7 @@ class PrinterUpdate(BaseModel):
     is_active: Optional[bool] = None
     protocol: Optional[str] = None
     line_width: Optional[int] = None
+    duplicates: Optional[int] = None
 
 
 class PrinterOut(PrinterBase):