fix(security): make allowFrom id-only by default with dangerous name opt-in (#24907)

* fix(channels): default allowFrom to id-only; add dangerous name opt-in

* docs(security): align channel allowFrom docs with id-only default

src/discord/monitor/message-handler.process.ts

@@ -199,6 +199,7 @@ export async function processDiscordMessage(ctx: DiscordMessagePreflightContext)
     channelConfig,
     guildInfo,
     sender: { id: sender.id, name: sender.name, tag: sender.tag },
+    allowNameMatching: discordConfig?.dangerouslyAllowNameMatching === true,
   });
   const storePath = resolveStorePath(cfg.session?.store, {
     agentId: route.agentId,