Problem: Wrong credentials during login produced two bugs: scrapers
wrapped the `bad_credentials` error code in `"Login failed: ..."`,
causing double-prefixed messages in the UI; and `credentials.lua`
did not clear cached credentials before re-prompting or on failure,
leaving stale bad creds in the cache.
Solution: Standardize all scrapers to emit `"bad_credentials"` as
the raw error code. Add `LOGIN_ERRORS` map in `constants.lua` to
translate it to a human-readable string in both `credentials.lua`
and `submit.lua`. Fix `credentials.lua` to clear credentials on
failure in both the fresh-prompt and cached-creds-fail paths.
For AtCoder and Codeforces, replace `wait_for_url` with
`wait_for_function` to detect the login error element immediately
rather than waiting the full 10s navigation timeout. Also add
"Remember me" checkbox check on Codeforces login.
Barrett Ruth
0ad7a9614f
