fix(listener): improve Discord delivery failure logging

[praizeD10]

• Replace duplicate success log with a single, richer delivery log
• Add classifyHttpStatus() to map status codes to readable categories (rate_limited, auth_error, not_found, client_error, server_error)
• Add safeReadResponseBody() to capture error bodies with 300-char cap
• Surface retryAfter header on 429 responses for actionable diagnostics
• Pass logContext through sendWebhook() so timeout logs carry requestId and eventId for end-to-end traceability
• Fix sendTestMessage() to log error detail on non-ok responses instead of a bare ok:true/false field
• Webhook URL and tokens never appear in any log path; only webhookId is logged
• Update e2e test assertions to match renamed log messages and new field names (httpStatus, httpCategory) in both delivery lifecycle and multi-channel test suites

Overview

Related Issue

Closes #638

Changes

Verification

# e.g.
cd dashboard && npm test
cd listener && npm run typecheck && npm test
cd contract/contracts/hello-world && cargo test

How to Test

Checklist

• Branch is up to date with main
• Tests added/updated and all pass locally
• cargo fmt --all run (if Rust changes)
• npm run lint passes (if TypeScript changes)
• Documentation updated if behavior changed

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