chore: add support for efficient domain-based operations for User and SecondaryEmail

[alishaz-polymath]

What does this PR do?

This PR introduces a schema change to support efficient domain-based operations without relying on string parsing or in-memory user ID lists at query time.

Specifically, it:

• Adds a nullable email_domain column to users and SecondaryEmail
• Introduces database triggers to automatically populate email_domain on future inserts and email updates
• Establishes a safe foundation for indexed, DB-side domain filtering without impacting existing rows or requiring backfill in this PR

This PR intentionally does not backfill existing rows to avoid long-running locks or table rewrites. Historical backfill and index creation will be handled separately.

Fixes #XXXX

Fixes CAL-XXXX

Visual Demo (For contributors especially)

N/A — database-only schema change with no UI or behavior changes exposed yet.

Mandatory Tasks (DO NOT REMOVE)

• I have self-reviewed the code (A decent size PR without self-review might be rejected).
• N/A I have updated the developer docs in /docs if this PR makes changes that would require a documentation change.
• I confirm automated tests are in place that prove my fix is effective or that my feature works.

How should this be tested?

This change is verified at the database level.

Manual verification steps:

• Insert a new user with an email containing a valid domain.
• Confirm email_domain is automatically populated with the lowercase domain portion.
• Update an existing user’s email and verify email_domain updates accordingly.
• Repeat the above for SecondaryEmail.

Expected behavior:

• New and updated rows correctly populate email_domain

• Existing rows remain unchanged (email_domain = NULL)

• No application-level logic is required to manage domain normalization

• Environment variables: None

• Minimal test data: A single user and secondary email record

• Happy path: email = [email protected] → email_domain = domain.com

Checklist

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3 Skipped Deployments

Project	Deployment	Review	Updated (UTC)
cal	Ignored		Jan 2, 2026 2:03pm
cal-companion	Ignored	Preview	Jan 2, 2026 2:03pm
cal-eu	Ignored		Jan 2, 2026 2:03pm

[alishaz-polymath]

Closing in Favor of alternate approach