feat(sdk+cli): bridge peer — forward a topic between two meshes

A bridge holds memberships in two meshes and relays messages on a
single topic between them. Federation-lite without a broker-to-broker
protocol.

SDK additions:
- Bridge class (start, stop, EventEmitter for forwarded/dropped/error)
- MeshClient.joinTopic / leaveTopic / createTopic methods
- Loop prevention: plaintext hop counter prefix __cmh<n>: with maxHops
  default 2; echo guard via senderPubkey == own session pubkey

CLI additions:
- claudemesh bridge run <config.yaml> long-lived process
- claudemesh bridge init prints config template
- Zero-dep YAML parser for the flat bridge config shape

The hop prefix is visible in message bodies — minor wart, fixed in
v0.3.0 by moving loop tracking into broker primitives.

SDK kept as devDependency since Bun bundles it into dist; no impact
on npm publish or runtime resolution.

Spec: .artifacts/specs/2026-05-02-v0.2.0-scope.md

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

apps/cli/src/entrypoints/cli.ts

@@ -107,6 +107,10 @@ API keys  (REST + external WS auth, v0.2.0)
   claudemesh apikey list             show keys (status, last-used, scope)
   claudemesh apikey revoke <id>      revoke a key
 
+Bridge  (forward a topic between two meshes, v0.2.0)
+  claudemesh bridge init             print config template
+  claudemesh bridge run <config>     run bridge as a long-lived process
+
 Topic  (conversation scope, v0.2.0)
   claudemesh topic create <name>   create a topic [--description --visibility]
   claudemesh topic list            list topics in the mesh
@@ -514,6 +518,23 @@ async function main(): Promise<void> {
       break;
     }
 
+    // bridge — forward a topic between two meshes (v0.2.0)
+    case "bridge": {
+      const sub = positionals[0];
+      if (sub === "run") {
+        const { runBridge } = await import("~/commands/bridge.js");
+        process.exit(await runBridge(positionals[1] ?? ""));
+      } else if (sub === "init" || sub === "config") {
+        const { bridgeConfigTemplate } = await import("~/commands/bridge.js");
+        console.log(bridgeConfigTemplate());
+        process.exit(EXIT.SUCCESS);
+      } else {
+        console.error("Usage: claudemesh bridge <run <config.yaml> | init>");
+        process.exit(EXIT.INVALID_ARGS);
+      }
+      break;
+    }
+
     // apikey — REST + external WS bearer tokens (v0.2.0)
     case "apikey": case "api-key": {
       const sub = positionals[0];