fix: user model findbyemailorusername options handling

[Nixxx19]

Issue:

Fixes #3911

The findByEmailOrUsername static on the User model currently uses arguments.length === 2 to decide when to apply case-insensitive behavior. This is fragile and can break if the function is called with default parameters or extra arguments. The behavior should instead be controlled explicitly via the options parameter.

Changes:

• Updated server/models/user.ts findByEmailOrUsername to:
  • Remove the arguments.length === 2 check.
  • Use an explicit, options-based condition: if (options && typeof options === 'object' && options.caseInsensitive).
• Kept the existing API shape: callers still pass an optional options object with caseInsensitive and valueType.

I have verified that this pull request:

• has no linting errors (npm run lint)
• has no test errors (npm run test)
• has no typecheck errors (npm run typecheck)
• is from a uniquely-named feature branch and is up to date with the develop branch. (nityam/fix-user-findbyemailorusername)
• is descriptively named and links to an issue number, i.e. Fixes #3911
• meets the standards outlined in the accessibility guidelines