Send a weekly digest to Slack

POST /api/v1/weekly-report collects everything published in the last seven
days, groups it by project and posts one message. dry=1 returns the message
instead of sending it, no publications means no message, a missing webhook
answers 501 instead of failing quietly. scripts/cron.mjs runs the due
publishing first, then the digest.

src/lib/slack.ts

@@ -0,0 +1,29 @@
+import type { SlackMessage } from './weekly-report'
+
+export type SlackResult =
+	| { ok: true }
+	| { ok: false, reason: 'not_configured' | 'rejected', detail?: string }
+
+export function slackWebhook(): string | undefined {
+	const url = process.env.SLACK_WEBHOOK_URL?.trim()
+
+	return url === '' ? undefined : url
+}
+
+export async function sendToSlack(message: SlackMessage, webhook = slackWebhook()): Promise<SlackResult> {
+	if (!webhook) {
+		return { ok: false, reason: 'not_configured' }
+	}
+
+	const response = await fetch(webhook, {
+		method: 'POST',
+		headers: { 'content-type': 'application/json' },
+		body: JSON.stringify(message),
+	})
+
+	if (!response.ok) {
+		return { ok: false, reason: 'rejected', detail: `${response.status} ${await response.text()}` }
+	}
+
+	return { ok: true }
+}