- Add CREDS_FILE/CREDS_MOUNT detection after mkdir ~/.claudebox
- Conditional --bind in exec bwrap via BWRAP_ARGS array
- Mirror conditional bind in --dry-run display block
- Read-write mount (not ro-bind) for OAuth token refresh
- Silent skip when credentials file absent (no error/warning)
- Refactor exec bwrap to BWRAP_ARGS array for conditional mount support
