Increase access and refresh token field length to 4096 (#1523)Fix: increase access and refresh token field length to 4096 (#1523)

[DarshanKumarGP]

This pull request increases the maximum length of the access_token and refresh_token fields in the SQLAlchemy OAuth account model from 1024 to 4096 characters.

OAuth2 providers using long JWT tokens (such as RS256 signed tokens from Auth0 or Authentik) have tokens that exceed the 1024 character limit, causing database errors with PostgreSQL (StringDataRightTruncation).

This fix allows storing longer tokens without truncation errors.

Closes #1523.