refactor: migrate to tonutils 2.0.0 and restructure codebase

- Migrate from tonutils 0.5.x to 2.0.0 API:
  - ToncenterClient → TonapiClient with NetworkGlobalID
  - tonutils.client → tonutils.clients
  - tonutils.wallet → tonutils.contracts.wallet
  - pub_key.as_hex property, wallet.balance nanotons
  - async with client context manager

- Centralize TON client init into initialize_ton_client() in wallet.py
- Move process_transaction logic into wallet.py, transaction.py re-exports
- Add WALLET_VERSION config (V4R2/V5R1, default V5R1)
- Add WALLET_CLASSES and SUPPORTED_WALLET_VERSIONS to constants.py
- Restore balance check before broadcasting
- Wait for seqno confirmation after transfer (120×2s) to prevent duplicate seqno

- Fix Fragment hash fetching: use browser navigation headers
- Remove accept-encoding from BASE_HEADERS (httpx handles decompression)
- Add cookies.example.json template
- Add cookies.json to .gitignore

app/utils/decoder.py

@@ -34,5 +34,5 @@ def clean_decode(payload: str) -> str:
     sl.load_uint(32)  # op code — always 0 for text comment
     result = sl.load_snake_string().strip()
 
-    logger.debug("Decoded result: %s", result)
+    logger.debug("Decoded payload: %s", result.replace("\n", " "))
     return result