Profile

Read the users and identities model and the settings page. Add a profile section with a display name and a username. Store a normalised lower-case form of the username under a unique constraint, so Ann and ann are one name, and allow a short set of characters. Reject reserved words such as admin and support and anything that clashes with the product's own routes. Say whether a name is taken as the user types and rate limit that check, but rely on the constraint rather than the check when saving. Ask me whether a changed username stays held back for a while and write the answer in docs/. Validate on the server and add tests.