Add Outbound Webhook Events Stub

[aji70]

Task: Add Outbound Webhook Events Stub

Overview

Platform events (new subscriber, new post) are not externally consumable. An outbox stub prepares for future integrations and partner webhooks.

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Goals

• Entity: WebhookEvent (eventType, payload, status: pending|delivered|failed, attempts, createdAt)
• Emit from subscribe + post publish: subscription.created, post.published
• GET /api/v1/admin/webhook-events?page&limit — admin-only
• Dev dispatcher logs payload (no HTTP call yet)

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Deliverables

• WebhooksModule + dispatcher hook into subscriptions/posts
• Admin list endpoint with RBAC
• Tests verifying event emission

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Acceptance Criteria

• Subscribe creates one subscription.created outbox row
• Post publish emits post.published with postId, creatorId, visibility
• Admin list requires admin role; non-admin gets 403
• Tokens/secrets never stored in payload
• At least 6 tests