chore(client, server, api, shared): fix clippy lints

feat(api): get /api/user for public user details

feat(schema, shared, api): move all types to shared, separate schema
 * schema is now stored in a separate crate to avoid dependency cycles
 * added note in README.md about handling unwraps

feat(api): login password verification

WIP(api): session management

fix(api): check if user exists before hashing password on registration

feat(api): reimpl user registration