LF-5197: Account deletion: add migration and update UserModel

[litefarm-pr-bot]

Description

Prior to this change, the users table had no deleted flag and no dedicated column for storing a Google OAuth subject identifier. SSO users were identified by their numeric Google sub stored directly as user_id, which conflates authentication identity with the application's primary key. To support migrating SSO users to UUID-based user_ids (part of LF-5193), the Google sub must be stored separately so it can continue to be used for identity lookup after the migration.

This PR adds a Knex migration that introduces deleted boolean NOT NULL DEFAULT false and google_sub varchar NULL to the users table. It backfills google_sub from user_id for all existing rows where user_id is numeric (i.e. current SSO users), then adds an index on google_sub to support efficient lookups. The UserModel jsonSchema is updated to recognise both new columns for validation, and both are added to the hidden array so they are stripped from API responses by default. Pre-existing @typescript-eslint/no-unused-expressions lint errors in the same file (short-circuit assignment idioms) are also fixed to keep the file passing ESLint.

Going forward, any new column added to users that should not appear in API responses must be listed in UserModel.hidden. The google_sub column is intentionally nullable so that non-SSO (email/password) users have a null value.

Implements sub-task LF-5197, part of LF-5193.

Jira link: https://lite-farm.atlassian.net/browse/LF-5197

Type of change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• This change requires a documentation update

How Has This Been Tested?

• Passes test case
• UI components visually reviewed on desktop view
• UI components visually reviewed on mobile view
• Other (please explain)

Migration and model changes reviewed in source code. No local database running; migration was not executed against a live DB. Pre-commit lint and Prettier hooks passed successfully on commit.

Checklist:

• I have commented my code, particularly in hard-to-understand areas
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• The precommit and linting ran successfully
• I have added or updated language tags for text that's part of the UI
• I have ordered translation keys alphabetically (optional: run pnpm i18n to help with this)
• I have added the GNU General Public License to all new files