feat(spv): verify the chain identity of a server on connect

After the handshake the wallet checks server.features genesis_hash and,
when the profile has checkpoints, the header at the highest checkpoint
not above the server's tip (mainnet shares Bitcoin's genesis, so the
checkpoint is what tells the chains apart). A server on another chain is
refused with WrongChainException and the next candidate is tried. Used by
the GUI, peer discovery, the CLI and the server probe. See ADR 0036.

USERGUIDE.md

@@ -834,6 +834,7 @@ Reset SSL certificates* — see
 | *Wallet already open in another instance of the application.* | Another running process holds this wallet's lock. | Close the other instance (GUI or CLI). |
 | *The TLS certificate of host:port has changed…* | Certificate pin mismatch — renewal or interception. | Read [12.2](#122-tls-certificate-pinning-tofu--read-before-fixing-a-certificate-error) **before** resetting certificates. |
 | Sync aborts, "server is not trustworthy" | A Merkle proof failed, or (mainnet) a block header did not chain back to a known checkpoint. | Switch to another server. Your local data is intact; the wallet refused the bad data. |
+| *The server host:port is not on the Palladium chain (different genesis or checkpoint)…* | The server answered, but serves another chain (or a fork) than the wallet expects. Nothing was synced from it. | Pick another server; the wallet moves on to the next known one on its own. See [12.3](#123-what-synchronization-actually-does). |
 | *Insufficient funds* with a non-zero balance | Funds are unconfirmed, under 6 confirmations, or immature coinbase; or the fee doesn't fit. | See [8.4](#84-why-insufficient-funds-can-appear-despite-a-visible-balance). Wait, or use Send all. |
 | Restored wallet shows zero balance | Wrong passphrase, wrong script type, or funds beyond the gap limit. | See [15.2](#152-restoring-step-by-step) — the coins are not lost. |
 | *Invalid mnemonic (wrong words or checksum)* | A word is misspelled, not on the BIP39 list, or the checksum fails. | Compare against your paper backup, word by word. |