feat: P3-T5 route resolution — find relay path to any fingerprint

RouteResolver queries PresenceRegistry to determine how to reach a target:
- Route::Local — connected to this relay
- Route::DirectPeer(addr) — on a directly connected peer relay
- Route::Chain(addrs) — multi-hop (structure ready, single-hop for now)
- Route::NotFound — not in any known relay

Protocol: added SignalMessage::RouteQuery { fingerprint, ttl } and
RouteResponse { fingerprint, found, relay_chain } for peer-to-peer
route queries over probe connections.

HTTP API: GET /route/:fingerprint returns JSON with route type + chain.

Relay handles incoming RouteQuery on probe connections: looks up locally,
replies with RouteResponse. TTL decremented for future multi-hop forwarding.

55 relay tests + 42 proto tests passing (7 new route tests).

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

crates/wzp-relay/src/lib.rs

@@ -15,6 +15,7 @@ pub mod pipeline;
 pub mod presence;
 pub mod probe;
 pub mod room;
+pub mod route;
 pub mod session_mgr;
 pub mod trunk;