[Test]: cover notification delivery helpers

[viiccwen]

Summary

Add deterministic unit coverage for Discord notification delivery helpers and staff notification formatting. All Discord and delay boundaries are mocked, so the suite runs without external API access.

Related Issue

Fixes #85

Type of Change

• Bug fix
• New feature
• Refactor
• Documentation
• Configuration or deployment
• Tests

Changes

• Add table-driven coverage for member delivery success/failure aggregation and mocked delivery delays.
• Cover Discord channel success statuses, failure statuses, and exceptions without network calls.
• Verify logging no-ops without configuration and delegates when configured.
• Expand staff-role and notification-format coverage for optional fields, recording flags, and long-outline truncation.

Testing

• Local tests or checks pass: make test (165 passed)
• Manual verification completed: make precommit and git diff --check
• Not tested; reason:

Impact Checklist

• Discord bot behavior checked, if affected
• MCP server behavior checked, if affected
• Webhook behavior checked, if affected
• Docker or compose changes checked, if affected
• Environment variables documented, if changed
• Logs do not expose secrets or sensitive data

Notes for Reviewers

This is a test-only change. Discord API functions and time.sleep are mocked, and all member fixtures use synthetic identifiers and addresses.