feat(bridge): forward reaction webhook events

[jack-arturo]

Summary

• Forward inbound WhatsApp reactions to WEBHOOK_URL as typed eventType: "reaction" webhook payloads.
• Preserve PR feat: capture inbound reactions and add /api/react endpoint #108 persistence behavior: reaction emoji stays in content, target message ID stays in filename / reactionToMessageId.
• Document the reaction webhook payload, including empty-emoji removal events.

Behavior

• Reaction add: reactionEmoji and content contain the emoji, reactionRemoved: false.
• Reaction removal: reactionEmoji and content are empty strings, reactionRemoved: true.
• Self-authored reactions honor the existing FORWARD_SELF setting.

Tests

• cd whatsapp-bridge && go test -count=1 ./...
• cd whatsapp-bridge && golangci-lint run
• git diff --check
• Live local add/remove reaction test with AutoHub webhook receiver: both events reached AutoHub as Reaction webhook received; no normal assistant reply path was triggered.

Companion

• AutoHub receiver PR follows separately and consumes this typed payload.

[Copilot]

Pull request overview

This PR adds forwarding of inbound WhatsApp reaction events to the configured webhook endpoint as a typed webhook payload (eventType: "reaction"), while preserving the existing persistence semantics introduced in PR #108 (emoji in content, reacted-to message ID in filename / reactionToMessageId).

Changes:

• Extend the webhook payload schema to support typed reaction events (eventType, reactionToMessageId, reactionEmoji, reactionRemoved) and add a dedicated SendReactionWebhook helper.
• Update message handling to forward inbound reactions to the webhook (including empty-emoji removal events) while honoring FORWARD_SELF.
• Add tests validating reaction webhook forwarding behavior (add, removal, self-forwarding disabled, and “no key” ignored) and document the reaction webhook payload in the README.

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 1 comment.

File	Description
whatsapp-bridge/webhook.go	Adds reaction-specific fields to the webhook payload and introduces SendReactionWebhook.
whatsapp-bridge/main.go	Forwards inbound reactions to the webhook after persisting them, respecting FORWARD_SELF.
whatsapp-bridge/main_test.go	Adds end-to-end tests ensuring reaction webhook forwarding works for add/remove and respects forward/self and missing-key behavior.
README.md	Documents the typed reaction webhook payload shape and removal semantics.

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