Fix Slack message_replied thread reply ingress

[gugu91]

Summary

Fixes #744.

• normalize Slack message_replied payloads so known broker/agent-created thread replies route like normal replies
• hydrate body-less known-thread/DM message_replied updates via conversations.replies, with safe warning logs on hydration failure
• preserve bot/noise filtering, channel type, legacy threaded-DM suppression, and block/file-only message bodies
• deduplicate normal threaded message events vs matching hidden message_replied updates before hydration/inbox enqueue

Validation

• pnpm --filter @gugu910/pi-slack-bridge test -- broker/adapters/slack.test.ts single-player-runtime.test.ts
• pnpm --filter @gugu910/pi-slack-bridge lint
• pnpm --filter @gugu910/pi-slack-bridge typecheck
• pre-push hook: pnpm lint && pnpm typecheck && pnpm test
• local code-reviewer subagent final verdict: Approve, no critical/warning findings

Notes

Slack public docs show message_replied as a hidden message subtype carrying thread/root summary fields plus a nested reply object; the fix accepts that current shape and falls back to precise thread hydration when the reply body is omitted.