fix: normalize platform ID at registration, not router lookup

Channel adapters prefix platform IDs with their channel type
(e.g. "telegram:123"). Normalize in register.ts so the DB always
stores the canonical format. Removes fallback lookup from router.

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

setup/register.ts

@@ -118,6 +118,13 @@ export async function run(args: string[]): Promise<void> {
     process.exit(4);
   }
 
+  // Chat SDK adapters prefix platform IDs with the channel type
+  // (e.g. "telegram:123", "discord:guild:channel"). Normalize here so
+  // the stored ID always matches what the adapter sends at runtime.
+  if (!parsed.platformId.startsWith(`${parsed.channel}:`)) {
+    parsed.platformId = `${parsed.channel}:${parsed.platformId}`;
+  }
+
   log.info('Registering channel', parsed);
 
   // Init v2 central DB