[6.3] Implement server-side conversation log storage

[jasminetay-moe]

As an Engineer, I want to implement server-side conversation log storage (query + AI response per session) so that query data is captured and available for domain owner review.

Acceptance criteria

• Every teacher query and AI response logged server-side per session
• Logs stored at correct classification level (data governance and retention handled on cloud infrastructure side)
• Access restricted to authorised users per 6.6

Dependencies

• 6.6 (access control must be in place before logs are accessible)

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📄 PRD: Part 6 — Glow CI PRD