Bind Nova Poshta API key to cash register (#3)

Each cash register stores its own encrypted NP API key. Status polling uses
register keys and binds an order to the register whose key sees the TTN as
its own (PhoneSender present); ETTN receipts are created from that register.
Migration 0008 moves the old NOVA_POSHTA_API_KEY into the default register.

Closes #3

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

backend/app/schemas/receipts.py

@@ -70,26 +70,34 @@ class ReceiptCreateResponse(BaseModel):
 # --- Кассы -------------------------------------------------------------------
 
 
+def _masked(encrypted: str) -> str:
+    try:
+        return crypto.mask(crypto.decrypt(encrypted))
+    except crypto.DecryptionError:
+        return "не расшифровывается — введите заново"
+
+
 class CashRegisterOut(BaseModel):
     id: uuid.UUID
     name: str
     fiscal_number: str | None
     license_key_masked: str
+    # None — ключ НП не задан: касса не опрашивает посылки и не получает заказы.
+    np_api_key_masked: str | None
     tax_codes: list[Any]
     is_active: bool
     is_default: bool
 
     @classmethod
     def from_register(cls, register: CashRegister) -> CashRegisterOut:
-        try:
-            masked = crypto.mask(crypto.decrypt(register.license_key_enc))
-        except crypto.DecryptionError:
-            masked = "не расшифровывается — введите заново"
         return cls(
             id=register.id,
             name=register.name,
             fiscal_number=register.fiscal_number,
-            license_key_masked=masked,
+            license_key_masked=_masked(register.license_key_enc),
+            np_api_key_masked=(
+                _masked(register.np_api_key_enc) if register.np_api_key_enc else None
+            ),
             tax_codes=register.tax_codes,
             is_active=register.is_active,
             is_default=register.is_default,
@@ -101,6 +109,7 @@ class CashRegisterCreate(BaseModel):
     fiscal_number: str | None = Field(default=None, max_length=64)
     license_key: str = Field(min_length=1, max_length=255)
     pin_code: str = Field(min_length=1, max_length=32)
+    np_api_key: str | None = Field(default=None, min_length=1, max_length=255)
     tax_codes: list[int | str] = Field(default_factory=list, max_length=2)
     is_default: bool = True
 
@@ -112,6 +121,7 @@ class CashRegisterUpdate(BaseModel):
     fiscal_number: str | None = Field(default=None, max_length=64)
     license_key: str | None = Field(default=None, min_length=1, max_length=255)
     pin_code: str | None = Field(default=None, min_length=1, max_length=32)
+    np_api_key: str | None = Field(default=None, min_length=1, max_length=255)
     tax_codes: list[int | str] | None = Field(default=None, max_length=2)
     is_active: bool | None = None
     is_default: bool | None = None