Introduces a credential mode for stored credentials and wire it to
per-remote URL resolution and operation flows. The UI, storage, and
remote interactions now track and persist the mode, enabling token
based auth alongside username/password credentials.
- Remote URL resolution now considers direction (pull/push) and mode
- Credential dialog, saving, and keychain handling updated to pass and
respect the mode
- Unique askpass scripts generated per invocation to avoid clashes