fix: Update CRC calc to use 0 init and full 16-bit stored value

src/teletext/models.py

@@ -82,8 +82,9 @@ class Page:
         Row 0: Skips first 8 bytes (Header/Control). Uses bytes 8-39.
         Rows 1-23: Uses all 40 bytes.
         Data is 7-bit (stripped parity).
+        Initial value: 0 (ETSI EN 300 706 9.4.1.2).
         """
-        crc = 0xFFFF
+        crc = 0
         poly = 0x1021
         
         # Helper to update CRC with a byte
@@ -135,13 +136,13 @@ class Page:
                     
                     if designation == 0:
                         # Packet 27/0
-                        # Checksum is in bytes 38 and 39
+                        # Checksum is in bytes 38 and 39.
+                        # ETSI EN 300 706: 8 bits of each byte are used.
                         if len(p.data) >= 40:
                             hi = p.data[38]
                             lo = p.data[39]
                             
-                            # Strip parity
-                            crc = ((hi & 0x7F) << 8) | (lo & 0x7F)
+                            crc = (hi << 8) | lo
                             return crc
                 except:
                     pass