fix(selfhost): wire WEBHOOKS queue binding for the Orb relay receiver

[JSONbored]

Summary

The Orb relay receiver (handleOrbRelay) calls c.env.WEBHOOKS.send() to enqueue relayed webhook events onto the dedicated webhook lane — the same path as GitHub's own webhook receiver. server.ts wired JOBS but not WEBHOOKS, so every brokered-relay event failed immediately with enqueue_failed (500), silently eating all forwarded events and preventing any reviews from running on a brokered self-host.

Both JOBS and WEBHOOKS map to the same in-process DurableQueue in self-host mode (all job types share one queue; the consumer handles them regardless of which binding sent them), so the fix is adding WEBHOOKS: backend.queue.binding alongside the existing JOBS alias.

Tests added for all handleOrbRelay branches: missing GitHub headers (400), unconfigured relay/no enrollment secret (404), invalid HMAC signature (401), WEBHOOKS queue failure (500 enqueue_failed), and the success path (202 queued on the WEBHOOKS lane).

Scope

• Self-host / Orb / broker path
• New public API or changed API signature
• DB schema / migration
• Auth / session / CORS path
• UI change
• Docs change

Validation

• npx vitest run test/unit/webhook.test.ts — 9 tests (4 existing + 5 new), all pass
• npm run test:ci — exit 0, full gate green

Safety

• No secrets, tokens, wallets, hotkeys, trust scores, or reward values introduced
• No auth/CORS changes; no public API surface changed
• Self-host only; the Cloudflare Worker deployment is unchanged (has real Queue bindings)

[superagent-security]

Superagent didn't find any vulnerabilities or security issues in this PR.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 95.36%. Comparing base (47593c4) to head (5474a5a).
✅ All tests successful. No failed tests found.

Additional details and impacted files

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  Coverage   95.36%   95.36%           
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  Files         191      191           
  Lines       20714    20714           
  Branches     7489     7489           
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  Hits        19753    19753           
  Misses        380      380           
  Partials      581      581           

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