refactor: replace panic with error returns and update maintenance
- Replace 9 panic() calls in smart_defaults.go with error returns
- Add ErrUnknownProfile error type for better error handling
- Update all callers (worker/config.go, tui/config.go, tui/cli_config.go, tui/main.go)
- Update CHANGELOG.md with recent WebSocket handler improvements
- Add metrics persistence, dataset handlers, and test organization notes
- Config validation passes (make configlint)
- All tests pass (go test ./tests/unit/api/ws)
3775bc3ee0