docs(governance): add meeting cadence

[Jo-anny]

Summary

Adds a dedicated meeting cadence document to the TeachLink Backend governance processes.

Changes

• Added Governance/processes/MEETING_CADENCE.md.
• Documented the meeting schedule and cadence.
• Defined the different meeting types and their purposes.
• Documented attendance and participation expectations.
• Kept the change self-contained within the Governance/ folder.

Scope

• Maximum of 2 files changed.
• No changes outside the Governance/ folder.
• No application functionality is modified.

Acceptance Criteria

• Governance requirement is documented.
• Meeting schedule and types are defined.
• Attendance expectations are documented.
• Changes are limited to the Governance folder.
• No existing functionality is affected.
• Documentation follows project standards.

closes #1584

[drips-wave]

@Jo-anny Great news! 🎉 Based on an automated assessment of this PR, the linked Wave issue(s) no longer count against your application limits.

You can now already apply to more issues while waiting for a review of this PR. Keep up the great work! 🚀

Learn more about application limits

[RUKAYAT-CODER]

Thank you for contributing to the project