Remove unused NetworkType::Trojan tombstone

The Trojan network type only ever existed as a non-runnable tombstone:
the SOCKS-era Trojan runtime it guarded against (BEP-0009) was never
merged to main, and no stored network uses it. Drop the enum value and
its dead match arms across the daemon, GTK summary, and Apple bindings.

The Trojan *protocol* outbound used by proxy-subscription nodes
(TrojanOutbound / ProxyOutbound::Trojan / isTrojanTCP) is unaffected.

- proto: remove `Trojan = 2`, add `reserved 2; reserved "Trojan";`
- daemon: drop ResolvedTunnel/ActiveTunnel::Trojan variants + match arms
  (runtime.rs) and the validate_network_payload arm (database.rs)
- gtk: drop the "Legacy Trojan Proxy" summary arm
- apple: drop the makeCard .trojan arm and regenerate the Swift
  NetworkType enum (case/rawValue/init/allCases/nameMap)

An unknown stored type now surfaces via the existing UNRECOGNIZED path.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

proto/burrow.proto

@@ -61,7 +61,8 @@ message Network {
 enum NetworkType {
     WireGuard = 0;
     Tailnet = 1;
-    Trojan = 2;
+    reserved 2;
+    reserved "Trojan";
     ProxySubscription = 3;
 }