feat: add TTI export functionality

src/teletext/io.py

@@ -228,3 +228,65 @@ def parse_header(data: bytearray):
     language = ((c_bits_2 & 1) << 1) | ((c_bits_2 & 2) >> 1) | (c_bits_2 & 4)
     
     return page_num, sub_code, language
+
+def save_tti(file_path: str, page: Page):
+    """
+    Saves a single Page object to a TTI file.
+    """
+    with open(file_path, 'w', encoding='latin-1') as f:
+        # Header Info
+        # DS - Source? Description?
+        f.write(f"DS,Teletext Editor Export\n")
+        f.write(f"SP,{file_path}\n")
+        
+        # PN - Page Number mpp00
+        # Typically TTI uses decimal integer for mppss? 
+        # Or mppss as hex digits? 
+        # Standard convention: mppss where m is 1-8, pp is 00-FF, ss is 00-99
+        # Example: Page 100 -> PN,10000
+        # Example: Page 1F0 -> PN,1F000
+        f.write(f"PN,{page.magazine}{page.page_number:02X}00\n")
+        
+        # SC - Subcode ssss
+        f.write(f"SC,{page.sub_code:04X}\n")
+        
+        # PS - Page Status
+        # 8000 is typical for "Transmission"
+        f.write(f"PS,8000\n")
+        
+        # RE - Region (Language)
+        f.write(f"RE,{page.language}\n")
+        
+        # Lines
+        # We need to construct the 40-char string for each row
+        # Row 0 is special (Header)
+        
+        # Get all packets for this page
+        # Map row -> packet
+        rows = {}
+        for p in page.packets:
+            rows[p.row] = p
+            
+        for r in range(26): # 0 to 25
+            if r in rows:
+                packet = rows[r]
+                # Packet data is 40 bytes (after the 2-byte header we stripped in Packet class? No wait)
+                # Packet.data in our model IS the 40 bytes of character data (we strip MRAG in __post_init__)
+                # So we just decode it as latin-1 to get the chars
+                
+                # However, we must ensure we don't have newlines or nulls breaking the text file structure
+                # TTI format usually accepts raw bytes 0x00-0xFF if strictly handled, but often expects
+                # mapped control codes.
+                # Standard VBIT2 TTI handling treats it as a binary-safe string if mapped to char.
+                
+                # Row 0 special handling: The first 8 bytes of Row 0 are usually header flags in the packet,
+                # but visually they are "P100    ".
+                # TTI usually expects the visual representation for the line content.
+                # But for transmission, we want the raw bytes.
+                # OL,r,String
+                
+                data_str = packet.data.decode('latin-1')
+                f.write(f"OL,{r},{data_str}\n")
+            else:
+                # Empty line? Usually omitted or written as empty
+                pass