feat: add hostname to hello + local/remote peer locality detection

Peers report os.hostname() in the hello handshake. list_peers shows
[local] or [remote] tag per peer. MCP instructions teach AI to read
local peers' files directly via filesystem instead of relay.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

apps/cli/src/ws/client.ts

@@ -35,6 +35,7 @@ export interface PeerInfo {
   sessionId: string;
   connectedAt: string;
   cwd?: string;
+  hostname?: string;
   peerType?: "ai" | "human" | "connector";
   channel?: string;
   model?: string;
@@ -194,6 +195,7 @@ export class BrokerClient {
               sessionId: `${process.pid}-${Date.now()}`,
               pid: process.pid,
               cwd: process.cwd(),
+              hostname: require("os").hostname(),
               peerType: "ai" as const,
               channel: "claude-code",
               model: process.env.CLAUDE_MODEL || undefined,