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.

docs/adr/README.md

@@ -39,6 +39,7 @@ One ADR per feature or significant design decision. Format: `template.md`. Workf
 | 0033 | [Test the UI layer and CLI headlessly, gate coverage](0033-test-strategy-beyond-core.md) | Testing | Accepted |
 | 0034 | [Bound every network request with a timeout](0034-bound-every-network-request.md) | Network | Accepted |
 | 0035 | [Cap the length of a server line](0035-cap-server-line-length.md) | Network | Accepted |
+| 0036 | [Verify the chain identity of a server right after connecting](0036-verify-chain-identity-on-connect.md) | SPV | Accepted |
 
 ADRs `0002` onwards were written retroactively on 2026-11-03 from the code, comments and changelog. 
 If one misstates the original reasoning, fix it in a pull request.