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

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One channel of #1963: deliver a formatted RecapReport to Discord as an embed, reusing the validated webhook + best-effort send pattern already in src/services/notify-discord.ts (isValidDiscordWebhook, the fetch+swallow at notify-discord.ts:75, and resolveWebhook / DISCORD_WEBHOOK_URL fallback at notify-discord.ts:28). Best-effort: a Discord outage must never break the recap job.

Deliverables

• deliverRecapToDiscord(env, report) in src/services/maintainer-recap.ts (or a delivery sibling) posting the formatted digest as an embed via the existing resolveWebhook path in src/services/notify-discord.ts:28
• No-op when no webhook is configured or the URL fails isValidDiscordWebhook (src/services/notify-discord.ts:10); swallow send errors like notify-discord.ts:76
• Unit test with a fetch stub: sends when configured, no-ops when unset/invalid, and never throws on fetch rejection (all branches)

References

• src/services/notify-discord.ts:10
• src/services/notify-discord.ts:28
• src/services/notify-discord.ts:75

Part of #1963.

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

[linear-code]

JSO-2346