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-proto/src/packet.rs

@@ -601,6 +601,18 @@ pub enum SignalMessage {
         /// Address of the sending relay (e.g., "192.168.1.10:4433").
         relay_addr: String,
     },
+
+    /// Ask a peer relay to look up a fingerprint in its registry.
+    RouteQuery {
+        fingerprint: String,
+        ttl: u8,
+    },
+    /// Response to a route query.
+    RouteResponse {
+        fingerprint: String,
+        found: bool,
+        relay_chain: Vec<String>,
+    },
 }
 
 /// Reasons for ending a call.