Add xync namespace (CAIP-2, CAIP-10, CAIP-19 profiles)

[mixartemev]

This PR registers the xync namespace: Xync Network, a
payments-only Layer-1 blockchain (send / request money in up to 255
protocol-native currencies; no VM). The namespace ships three CAIP
profiles following _template:

• CAIP-2 — human-readable network references declared in genesis
  (xync:main, xync:dev-1); resolution via any validator's
  GET /status, genesis SHA-256 co-signed by the checkpoint quorum.
• CAIP-10 — accounts are protocol-issued integer indexes
  (xync:main:518-K7). Keys are rotatable, so the index is the stable
  identifier; an optional 2-char Crockford-base32 checksum suffix is
  required in user-facing forms (the index space is dense, so typo
  protection matters more than in hash-address namespaces; the
  checksum also binds the CAIP-2 id, catching testnet/mainnet mixups).
• CAIP-19 — assets are single-byte registry codes
  (xync:main/cur:0 = the native token XYNC; cur:1 = issuer-backed
  USD), resolvable via GET /currencies.

The network runs a live payment product (XyncPay, Telegram MiniApp)
currently completing progressive decentralization; the reference
implementation and the yellow paper are linked from the profiles.