#23356: feat(slack): pass agent identity via chat:write.customize

## Summary - Wire `resolveAgentOutboundIdentity` into all `deliverOutboundPayloads` call sites so agent identity (`name`/`emoji`/`avatar`) is forwarded to channels that support it (e.g. Slack `chat:write.customize`) - The Slack send path already handles `SlackSendIdentity` and gracefully falls back when the scope is missing — this change just ensures the identity data actually reaches it - Follows the existing pattern used by the cron isolated-agent runner **5 call sites updated:** - `src/auto-reply/reply/route-reply.ts` — main auto-reply flow - `src/commands/agent/delivery.ts` — CLI agent delivery - `src/infra/heartbeat-runner.ts` — heartbeat OK + heartbeat delivery (2 calls) - `src/gateway/server-methods/send.ts` — gateway send method - `src/gateway/server-node-events.ts` — node event delivery ## Test plan - [x] `pnpm check` passes (format + lint + types) - [x] `pnpm build` succeeds - [x] All 1249 unit tests pass (0 failures) - [x] Existing `slack.test.ts` tests verify identity forwarding works - [ ] Manual verification: configure multi-agent setup with `identity.name` + `identity.emoji`, confirm Slack messages show per-agent identity Closes #23325