feat(notifications): Slack delivery for the maintainer recap digest (reuse notify-discord Slack path)

[JSONbored]

The Slack channel of #1963: deliver the formatted RecapReport to Slack via a Block Kit section, reusing the existing Slack sender scaffolding in src/services/notify-discord.ts — isValidSlackWebhook (notify-discord.ts:83), escapeSlackMrkdwnText (notify-discord.ts:93), and the SLACK_WEBHOOK_URL binding already declared at src/env.d.ts:131. Best-effort, sibling of the Discord recap delivery.

Deliverables

• deliverRecapToSlack(env, report) posting the digest as a Block Kit mrkdwn section via the SLACK_WEBHOOK_URL path (src/env.d.ts:129)
• Reuse isValidSlackWebhook + escapeSlackMrkdwnText from src/services/notify-discord.ts:83; no-op when unset/invalid; swallow errors like notify-discord.ts:117
• Unit test with a fetch stub: mrkdwn escaping (& < >), no-op-when-unset, and never-throws (all branches)

References

• src/services/notify-discord.ts:83
• src/services/notify-discord.ts:93
• src/env.d.ts:129

Part of #1963.

---

size: S · held for later release (gittensor:feature once activated)

[linear-code]

JSO-2347