refactor: moved hashing logic into application layer for security;

fix: error handling in auth service for database;
refactor: removed redundant taken email check;
chore: removed todos that were completed/not needed;
fix: leaking transactions in complete registration and login on error;
refactor: got rid of txless requests during transactions;

sqlc/query.sql

@@ -39,7 +39,7 @@ SELECT users.* FROM users
 JOIN login_informations linfo ON linfo.user_id = users.id
 WHERE linfo.email = @email::text;
 
-;-- name: GetUserByLoginCredentials :one
+;-- name: GetValidUserByLoginCredentials :one
 SELECT
   users.id,
   users.username,
@@ -88,7 +88,7 @@ WHERE users.username = $1;
 
 ;-- name: CreateLoginInformation :one
 INSERT INTO login_informations(user_id, email, password_hash)
-VALUES ( $1, $2, crypt(@password::text, gen_salt('bf')) ) RETURNING *;
+VALUES ( $1, $2, @password_hash::text ) RETURNING *;
 
 ;-- name: UpdateLoginInformationByUsername :exec
 UPDATE login_informations
@@ -118,9 +118,9 @@ WHERE users.username = $1;
 
 ;-- name: CreateConfirmationCode :one
 INSERT INTO confirmation_codes(user_id, code_type, code_hash)
-VALUES ($1, $2, crypt(@code::text, gen_salt('bf'))) RETURNING *;
+VALUES ($1, $2, @code_hash) RETURNING *;
 
-;-- name: GetConfirmationCodeByCode :one
+;-- name: GetValidConfirmationCodeByCode :one
 SELECT * FROM confirmation_codes
 WHERE 
   user_id = $1 AND