Fix exit node REPL blindness and hostname resolution

[maxholman]

Fix exit node REPL blindness and hostname resolution

Scope

Exit node peer lifecycle (registration/deregistration in shared Registry),
IPC address parsing, and the NodeApi trait boundary between IPC and daemon.

Crates: crates/daemon/src/mode/exit.rs, crates/core/src/ipc.rs,
crates/core/src/control/handler.rs, and the NodeApi trait.

Out of scope

• REPL output formatting/colours (bugs 1+2 from TODO.md "Random" section — separate task)
• Tracing subscriber changes (logfmt for wallhackd/systemd, consistent prefixed for REPL — separate task)
• Entry node connect path (already works)
• TUN EBUSY lifecycle bug
• New features, performance work

Why

The REPL is non-functional on exit nodes — three related bugs:

1. Peers invisible (TODO "Random" bugs 3+4): run_exit_loop never calls
   peers.register(), so PeerConnected notifications never fire and peers
   always returns empty. The entry node does this correctly — the exit connect
   path was never wired up.

2. Hostname rejected (TODO "Random" bug 5): The IPC connect command does
   req.addr.parse::<SocketAddr>() which rejects bare hostnames. The CLI
   --connect path goes through AddressSpec + DNS resolution, but the REPL
   bypasses both. Users cannot connect attacker from the REPL.

Notes

• No new dependencies. All fixes must use what's already in the workspace.
• The Registry needs to be threaded through to run_exit_loop — currently
  exit::run() takes metrics: &Arc<Metrics> but no peers. Follow the
  entry node pattern in entry.rs where conn_peers.register() /
  conn_peers.unregister() bracket the connection lifecycle.
• For the hostname bug, the IPC dispatcher needs DNS resolution before calling
  api.connect(). Options: (a) resolve in the dispatcher and keep
  NodeApi::connect(SocketAddr), (b) change the trait to accept AddressSpec
  or String and resolve inside the implementation. Option (a) is less
  invasive. Either way, default port injection via apply_default_port (or
  equivalent) is needed so bare hostnames work.
• The exit node's Handler currently returns NotSupported for connect() —
  this also needs to become functional if we want REPL connect to work on
  exit nodes.