- internal/db/db.go: Use _pragma syntax so modernc.org/sqlite actually
applies busy_timeout(5000) and journal_mode(WAL). Eliminates SQLITE_BUSY
500s when concurrent reads hit a writer holding the DELETE-mode lock.
- internal/api/handlers_*.go: Add slog.Error before every writeError with
StatusInternalServerError so real errors appear in logs (30+ sites across
handlers_jobs, handlers_machines, handlers_syncpairs, handlers_sshkeys).