Update DB schema

[devakesu]

No description provided.

[Copilot]

Pull request overview

This PR updates the Supabase/Postgres schema to tighten constraints, improve RLS policies, and add performance-related extensions and indexes.

Changes:

• Enables hypopg and index_advisor extensions and adds B-tree indexes on contact_messages.user_id and notification.auth_user_id to support query performance and index analysis.
• Refines core tables (users, tracker, notification, user_settings, contact_messages) with table comments, a new unique_attendance_slot constraint for tracker, and makes users.terms_version non-nullable to align with application logic.
• Adjusts RLS policies to use auth.uid() via a subselect and sets the search_path for the delete_user_account function to public for more predictable execution.

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