Source Control: Unverified is forgotten on every host restart #713

#707 records which saved credential has answered a 2xx only in the host process (worked map). After every restart every saved GitLab or Azure PAT and every Bitbucket access token shows the "hasn't used this token yet" notice again until a pull request is read with it and Source Control is reopened. Expected: remember the verified fingerprint with the credential (settings secrets or a small per-host file), clear it when the token changes or is rejected, and recompute the status when the first read succeeds rather than only when the page opens. Owner: the three hosts' credential_status in crates/services/src/{gitlab,azure,bitbucket}/mod.rs and the settings store.